exogenous pathway of antigen presentation occurs in association with

They both comprise two α- and β-chains from different sources. Image: MHC class I presents peptides to CD8, Image: MHC class II presents peptides to CD4. Scopus. The initial part of the locus codes for MHC protein class II, while the latter part codes for MHC protein class I. In some cases, peptides fail to associate with MHC class I and they have to be returned to the cytosol for degradation. It should be noted that 30–70% of proteins are immediately degraded after synthesis (they are called DRiPs – defective ribosomal products, and they are the result of defective transcription or translation). In these locations, respective lymphocytes are exposed to every antigen in the fetus. Aside from the proteinaceous antigens, some cells also possess lipid antigens (see image below). These partially folded MHC class I molecules are then associated with a TAP via another protein called tapasin. Already registered? This is carried out by Antigen-presenting cells (APCs), the most important of which are dendritic cells, B cells and macrophages. Conversion to peptides of exogenous Antigens (endocytic path) and endogenous Antigens (cytosolic path) Students: Educators’ Pro Tips for Tough Topics, Institutions: Ensure Medical Teaching Continuity. Class I-restricted processing and presentation of exogenous cell-associated antigen in vivo. This pathway is used for the MHC class I molecules associated with endogenous antigens (see image below). Human MHC class I molecules are encoded by a series of genes – HLA-A, HLA-B and HLA-C (HLA stands for ‘Human Leukocyte Antigen’, which is the human equivalent of MHC molecules found in most vertebrates). Cross presentation occurs when an antigen made outside the APC is internalized by endocytosis or phagocytosis, and instead of complexing with class II MHC, it is routed to a compartment containing class I MHC (see Fig. As the exogenous pathway can involve infection before presenting the antigens, the cross-presentation allows dendritic cells to process and present antigens without being infected. This allows the antigens to stimulate different T cells: the endogenous antigens stimulate the helper T cells via class II molecules and the exogenous antigens cross-stimulate the cytotoxic T cells via the class I molecules. Some of these are bound to the B cell surface and serve as the cell’s antigen receptor. Janeway, Travers, Walport and Shlomchik. Once these MHC class II molecules combine with antigens and are displayed on the surface of antigen-presenting cells, they activate T helper (Th) cells. T cells need their antigens to be presented as short peptides, bound to special major histocompatibility complex (MHC) molecules. Strict editorial standards and an effective quality management system help us to ensure the validity Furthermore, they can present internalized antigens in association with either class I or class II MHC molecules (cross presentation), although the predominant pathway for internalized antigen is the class II pathway. License: CC BY 4.0. The discharge of antibodies, which bind pathogens in extracellular spaces of the body, is the fundamental effector capacity of B cells. There is also so called cross-presentation in which exogenous antigens can be presented by MHC class I molecules. Lipid antigens are presented by CD1 molecules, however. There they present their antigens to the T cells and natural killer cells. Peptides from within vesicles associated with class II MHC are recognized by Th cells. Some MHC class I molecules never bind peptides and they are also degraded by the ER-associated protein degradation (ERAD) system. Pathogens that manage to survive and thrive intracellularly (such as Mycobacterium tuberculosis), can proliferate in a way that allows their escape from presentation by an MHC molecule. Image: The diversity of the MHC. This process results in the formation of lymphocytes that are complementary to every antigen, even those of the fetus. Later, the CLIP is exchanged for an antigenic peptide derived from a protein degraded in the endosomal pathway. Those HLA antigens that correspond to MHC class II molecules include HLA-DP, DQ, DR, DM, DOA, and DOB. They present those antigens that are present in the cellular cytoplasm. Publisher Rockefeller University Press. Exogenous antigen pathway processing o Processing of exogenous antigens occurs within the endocytic or phagocytic vesicle o After internalization, the endosome (or phagosome) fuses with the lysosome o The lysosome contains proteases (cathepsins) & hydrolytic enzymes o Fusion with the lysosome creates the endolysosome or the phagolysosome They have the ability to look “into” and destroy other host cells if the latter are This allows the second messenger systems to come into play, which in turn activates the T cells (see images below). APCs can phagocytose and/or endocytose antigen, endosomally process it, and present it in association with MHC-II molecules (Ref. By: Lecturio. Four Pathways of Lipid Antigen Presentation. Login. Thus, peptide presented in complex with MHC class I can only be recognised by CD8+ T cells. All rights reserved. The antigen peptide from the external protein associates with the MHC II molecule in the channel between the α-1 and β-1 domains. These genes are highly polymorphic, which means that each individual has his/her own HLA allele set. Initially, proteins are phagocytosed and broken down by proteases in endosomes into peptides that are approximately 15 amino acids long (see image below). There is also so called cross-presentation in which exogenous antigens can be presented by MHC class I molecules. By: SanderB. There are different proteasomes that generate peptides for MHC class-I presentation: 26S proteasome, which is expressed by most cells; the immunoproteasome, which is expressed by many immune cells; and the thymic-specific proteasome expressed by thymic epithelial cells. Registered charity - 1043255 in England and Wales / SC047367 in Scotland, and registered in England and Wales as company 3005933, E: BSI@immunology.org Image: T lymphocytes within myocardium. Exogenous antigens include bacteria and toxins and these antigens are engulfed by the antigen presenting cell. MHC class I molecules (see images below) consist of a heavy α-chain spanning the membrane, which is coded by MHC genes, while the β-chain is a light chain and is produced by the β-microglobulin gene. The different MHC proteins are coded by the MHC gene, which is located on chromosome 6 (see image below). Exogenous, non-replicating antigens, such as soluble proteins, usually fail to enter the class I pathway of antigen processing and presentation. There does not seem to be a unique pathway for cross-presentation but rather different potential mechanisms of cross-presentation have been proposed. Two separate properties of MHC molecules make it impossible for pathogens to avoid them. By: Cannons Law Firm, Glasgow, UK. It delivers cytosolic peptides into the endoplasmic reticulum (ER), where they bind to nascent MHC class I molecules. This interaction is a part of so-called ‘three-signal activation model’, and actually represents the first signal. Present on all nucleated cells in the body, Present on professional antigen-presenting cells (dendritic cells, macrophages, B cells) and on thymic epithelium. By: OpenStax College–Anatomy & Physiology, Connexions website. When a lymphocyte reacts, it is killed immediately. These molecules are responsible for presenting antigens that are present extracellularly. The lymphocytes that remain will only attack foreign antigens. Tapasin interacts with the transport protein TAP (transporter associated with antigen presentation) which translocates peptides from the cytoplasm into the ER. Antigen presentation that results in CD8 + T cell activation is now named cross-priming (Bevan, 1976), whereas T cell deletion or induction of anergy is called cross-tolerance (Albert et … NCLEX®, NCLEX-RN®, and NCLEX-PN® are registered trademarks of the National Council of State Boards of Nursing, Inc (NCSBN®). Once inside the cell, these antigens are digested by enzymes and combined with the Class II MHC molecule. PGRpdiBpZD0idmlkZW8tcG9wdXAtMSIgc3R5bGU9IndpZHRoOiAxMDAlOyBoZWlnaHQ6IDEwMCU7Ij48aWZyYW1lIHdpZHRoPSIxMDAlIiBoZWlnaHQ9IjEwMCUiIHNyYz0iaHR0cHM6Ly93d3cueW91dHViZS5jb20vZW1iZWQvdzZQMFVrVDlZSzA/cmVsPTAmY29udHJvbHM9MCZzaG93aW5mbz0wIiBmcmFtZWJvcmRlcj0iMCIgYWxsb3dmdWxsc2NyZWVuPjwvaWZyYW1lPjwvZGl2Pg==. Viral and plasmid‐encoded proteins are processed via the TAP‐dependent intracellular pathway and presented in association with MHC class I molecules. Like the MHC class I heavy chain, human MHC class II molecules are encoded by three polymorphic genes: HLA-DR, HLA-DQ and HLA-DP. There is no clear differentiation between the endogenous and exogenous pathways. Antigen presenting cells (macrophages, dendritic cells, and B cells) degrade ingested exogenous antigen into peptide fragments within the endocytic processing pathway. At the same time, chaperone proteins within the rough endoplasmic reticulum help facilitate the proper folding of MHC class I molecules and β2-microglobulin. This is called antigen processing (see image). http://cnx.org/content/col11496/1.6/, Jun 19, 2013. These peptides are then combined with MHC molecules and expressed on the cell surfaces. The resulting MHC II-peptide complex proceeds to the surface, where it is expressed, ready for antigen presentation. Initially, due to the great diversity of DNA splicing and recombination, the immune system creates billions of different antibodies with a limited number of genes by rearranging DNA segments during B cell development, prior to antigen exposure. MHC class I presentation of exogenous antigens by APCs can occur via at least 2 distinct mechanisms. The body is capable of expressing both lipid and protein antigens. … These receptors are specific for specific antigens and bind the antigen attached to the MHC molecules, thereby stabilizing it. The second type of antigen presenting cell is the macrophage. Image: Presentation of lipid antigens by CD1. and high relevance of all content. Endogenous antigens can also be presented by MHC class II when they are degraded through autophagy. First, MHC is polygenic, as it contains a few distinctive MHC class I and MHC class II qualities; every individual has an arrangement of MHC molecules with varying specificities for different peptides. The proteasomes break these antigenic proteins into small peptides approximately 8–9 amino acids long; these are, in turn, transported with the transporter associated with antigen processing (TAP) complex into the endoplasmic reticulum. By: Lecturio. Antigen presentation is a vital immune process that is essential for T cell immune response triggering. Source Title Journal of Experimental Medicine. Antigens processed via the exogenous pathway are presented on MHC class II and activate CD4 + Th cells. Allergies (Allergic Diseases) and Atopy (Atopic Syndrome) — Pathophysiology and Most Common Diseases. TAP is a member of the ATP-binding-cassette transporter family. MHC class I complexes at the cell surface may dissociate as time passes and the heavy chain can be internalised. 8 & 9). start your immunology course now for free! Molecules recognized by antibodies, or by T Cells (as peptides presented via MHC complex on host cells); Possible Antigens include proteins, nucleic acids, lipids, complex carbohydrates; Antigen Processing. MHC molecules have the most polymorphic qualities known. The Exogenous Pathway This pathway is for the MHC class II molecules and is used by the antigen-presenting cells. Figure 1. The method of antigen processing occurs in two distinct ways, one for each type of antigen. Image: Presentation of lipid antigens by CD1. MHC class II molecules contain two chains that span the membrane; they are both coded for by MHC genes. Image: Summary schematic representation of MHC class II molecule, consisting of two α-domains and two β-domains. mouse processing of exogenous Hepatitis B surface antigen (HbsAg), VLP, occur in endolysosomal compartment that bind to MHC class l Ld molecules and are presented to CD8+ CTL. These include dendritic cells, macrophages, and B lymphocytes. By: Lecturio. Exposed peptide fragments capable of associating with the MHC binding grove. The complex of TAP, tapasin, MHC class I, ERp57 and calreticulin is called the peptide-loading complex (PLC). They are transported to the endoplasmic reticulum, where they are processed to form small peptides. MHC class II complexes consists of α- and β-chains that are assembled in the ER and are stabilised by invariant chain (Ii). Register to leave a comment and get access to everything Lecturio offers! Antigen-presenting cells are of three types, but the majority of them include dendritic cells. Without the invariant chain, the alpha and beta proteins will not associate. The groove is known as a peptide-binding groove. Antigens processed via the endogenous pathway are presented on MHC class I and activate CD8 + Tc cells. B. However, these lymphocytes are stored in numerous peripheral and central lymph node organs in an inactive state. Image: Endogenous antigen processing and presentation. Your email address will not be published. Early evidence supports the notion that cell-associated antigens are a physiological substrate for cross-presentation. This complex is packaged into a vesicle and moves to the cell surface during antigen presentation to helper T-lymphocytes. By: Lecturio. The peptide-binding groove is situated between domains α1 and β1. This is because transplanted cells can act like regular antigens and stimulate an adaptive immune response. Different MHC class II alleles can be used as genetic markers for several autoimmune diseases, possibly owing to the peptides that they present. This process involves two distinct pathways for processing of antigens from an organism's own (self) proteins or intracellular pathogens (e.g. This is possibly due to the presence of ER aminopeptidase (ERAAP) associated with antigen processing. Download. Before moving to the cell surface, the vesicle containing this complex fuses with the endosome containing the antigen peptides. Here, the invariant chain is proteolytically degraded and only a small part, the CLIP, remains attached to the peptide-binding groove. The protein antigens are presented by MHC molecules, which are coded by a specific segment of DNA. Soluble antigens destined for cross-presentation are taken up by distinct endocytosis mechanisms which route them into stable early endosomes and then to the cytoplasm for proteasomal degradation and peptide loading. Image: Exogenous antigen processing and presentation. There is also an interaction between the CD8+ molecule on the surface of the T cell and non-peptide binding regions on the MHC class I molecule. d. All of the above are correct. Image: Endogenous antigen processing and presentation. This array is interpreted by cytotoxic T lymphocytes and Natural Killer cells, allowing them to monitor the events inside the cell and detect infection and tumorigenesis. In order to be capable of engaging the key elements of adaptive immunity (specificity, memory, diversity, self/nonself discrimination), antigens have to be processed and presented to immune cells. Immunoglobulins of similar antigen specificity are released into the extracellular fluid as an immune response by mature B cells, the plasma cells. By: Scray. These can include foreign proteins, self-proteins, viral proteins, and others. The body’s lymphocytes then mature and T cells are carried to the thymus, while B cells are sent to the bone marrow for further processing. Macrophages are stimulated to eliminate micro-organisms in their intracellular vesicles, and B cells are stimulated to deliver antibodies that kill extracellular pathogens. Topic 9 Antigen Processing and Presentation . Abstract Class I and class II MHC molecules bind peptides during their biosynthetic maturation and provide a continuously updated display of intracellular and environmental protein composition, respectively, for scrutiny by T cells. TAP translocates peptides of 8 –16 amino acids and they may require additional trimming in the ER before binding to MHC class I molecules. This is due to the presence of small glycoprotein antigens on the surface of the invading organisms, which the body identifies as foreign. Peptides escaping from the exogenous pathway may be displayed on MHC class I via cross-presentation. The MHC class I antigen-presentation pathway. This chain, which trimerizes in the ER, associates with MHC class II molecules and is released from the ER as a 9-subunit complex. As opposed to MHC class I, MHC class II molecules do not dissociate at the plasma membrane. This pathway probably involves uptake of antigen into endocytic vesicles, alteration of antigen within an intracellular compartment, and subsequent display of antigen on the presenting cell surface (Unanue 1984). Results as a consequence of the exogenous pathway, cross presentation or the endogenous pathway. The immune system is equipped to fight foreign invaders via complex and intricate processes. When peptides bind to MHC class I molecules, the chaperones are released and peptide–MHC class I complexes leave the ER for presentation at the cell surface. Image: Polymorphism of MHC class I and II molecules. Once foreign organisms are phagocytosed, they form an endosome, which is fused with lysosomes that contain enzymes to kill and digest the organisms. When a foreign organism invades the body, the immune system receives an alert. Prior to entering the ER, peptides are derived from the degradation of proteins, which can be of viral- or self origin. © An antigen needs to be transported to the lymphocytes in order to trigger their activation. The usual process of antigen presentation through the MHC I molecule is based on an interaction between the T-cell receptor and a peptide bound to the MHC class I molecule. T cells co-evolved with B cells. Receptor-mediated endocytosis, phagocytosis, and macropinocytosis all contribute to antigen uptake by class II MHC-positive antigen-presenting cells. However, T cells do not recognize antigens in the same way that B cells do. Thus, only those antigens that have been broken down into peptides will be effective in eliciting a response. Surface-associated MHC class I heavy chain (HC) molecules are involved in the alternative processing and presentation pathway of exogenous HBsAg10,11. This process requires the chaperone HLA-DM, and, in the case of B cells, the HLA-DO molecule. Once the antigens are presented on the cellular surface and bound to the MHC molecules, they need to activate the T cells. By: Lecturio. On the surface of a single cell, MHC class I molecules provide a readout of the expression level of up to 10,000 proteins. 10-14 Antigens derived from many sources, for example, soluble proteins, immune complexes, and protein-coated beads, can be conveyed from the endocytic compartment into the cytosol in APCs. 344. The interferon-γ (IFNγ)-IRF1 signaling pathway regulates MHC class I antigen presentation… Read more about the editorial team, authors, and our work processes. Thereafter, the process of antigen presentation by means of MHC class II molecules basically follows the same pattern as for MHC class I presentation. APCs can digest proteins they encounter and display peptide fragments from them on their surfaces for another immune cell to recognise.This process of antigen presentation allows T … Author Carbone, FR; Bevan, MJ. B lymphocytes ("B cells"); which are responsible for producing antibodiesagainst the antigen. T cells, on the other hand, have antigen-recognizing proteins on their cell membrane, called T cell receptors (TCRs). Some of the MHC class I molecules can be recycled and present endosomal peptides as a part of a process which is called cross-presentation. This MHC-invariant complex passes from the RER to, and out of, the Golgi body. Sign up to get access to 250+ video lectures for free! 9.2).43,44 At least one pathway involves proteosome digestion and complexing of the peptide with class I in the ER in the usual manner. Immunobiology. The difference is that the peptides originate from different sources – endogenous, or intracellular, for MHC class I; and exogenous, or extracellular for MHC class II. The process begins by phagocytosis of the antigens into the cell. As noted, HLA antigens are the MHC molecules. Exogenous/extracellular antigens are internalized by APCs such as macrophages, dendritic cells and B-cells. These molecules have a unique binding structure that allows them to bind to and present a wide variety of lipid antigens. MHC class I and class II molecules are similar in function: they deliver short peptides to the cell surface allowing these peptides to be recognised by CD8+ (cytotoxic) and CD4+ (helper) T cells, respectively. Instead, the body employs CD1 molecules, which are a non-polymorphic family of glycoproteins that are capable of presenting lipid antigens to T cells. Which statement(s) correctly describe antigen generation. Because T cells recognise only fragmented antigens displayed on cell surfaces, antigen processing must occur before the antigen fragment, now bound to the major histocompatibility complex (MHC), is transported to the surface of the cell, a process known as presentation, where it … MCAT is a registered trademark of the Association of American Medical Colleges (AAMC). T cells can only recognise antigens when they are displayed on cell surfaces. Invading foreign organisms are ingested by antigen-presenting cells. This exogenous presentation pathway is the well-recognized route of presentation of soluble and particulate antigens to T lymphocytes. Those HLA antigens that correspond to MHC class I molecules include HLA-A, B, and C. Peptides from the cytosol associated with class I MHC are recognized by Tc cells. License: CC BY 3.0. MHC II molecules appear to be expressed on the surface of cells in pairs. In the rough ER, the naïve MHC class II molecules  (alpha and beta chains) associate with each other, and a third protein, called the invariant chai, stabilizes the complex. All cells carry antigens on their surface; the body can distinguish the different self- and non-self-antigens because of the selection process during birth and in the early years of life. The outcome is often injurious to the pathogens, with the common sequelae of infected cells being killed. There are two major classes of MHC molecules, each with their own characteristics and functions (see table above). Exogenous Antigens: The Endocytic Pathway Whether an antigenic peptide associates with class I or II molecules, is dictated by the mode of entry into the cell, (Exo/Endo), and by the site of processing. The complex of MHC class II and Ii is transported through the Golgi into a compartment which is termed the MHC class II compartment (MIIC). These polypeptides can gain access to the exogenous processing pathway in phagocytic cells if they are soluble. License: Public domain. MHC class I molecules are present on all nucleated body cells. Image by Lecturio. the hard work of our editorial board and our professional authors. WANT TO SWITCH TO VIDEO LECTURES RIGHT NOW? Overview of Antigen Processing Pathways. B, Summary schematic representation of MHC class II molecule, consisting of two α-domains and two β-domains. Image: Exogenous antigen processing and presentation. Image: Polymorphism of MHC class I and II molecules. To ensure the attachment and action of these antigens, the T cells possess TCRs. There does not seem to be a unique pathway for cross-presentation but rather different potential mechanisms of cross-presentation have been proposed. Antigens are conserved, however. These proteins are created by B cells in an array of antigen specificities, with every B cell delivering a specific immunoglobulin. Published version (636.7Kb) Citations. MHC class I molecules are expressed by all nucleated cells. These antigens are presented to the T cells via specific molecules that are present on the antigen-presenting cells. Introduction. The small pieces of lipid antigens are mixed and bound with CD1 molecules, which are then exocytosed to the cell surface. Your email address will not be published. The mechanisms that control MHC class II degradation have not been established yet, but MHC class II molecules can be ubiquitinised and then internalised in an endocytic pathway. Thus, humans usually do not have lymphocytes that correspond to self-antigens. Only then will the antigens be effective and have the ability to activate the T cells. Image: MHC class II presents peptides to CD4+ helper or regulatory T cells. The consequences of these polymorphisms are differential susceptibilities to infection and autoimmune diseases that may result from the high diversity of peptides that can bind to MHC class I in different individuals. Second, MHC is profoundly polymorphic; ie, there are multiple variants of every gene, giving rise to incredible diversity within the population (see image above and below). MHC molecules are part of the HLA antigen group. b. In this lesson we will look at the two ways in which foreign antigens are processed prior to presentation to the cells of the immune system. Recognition of major histocompatibility complex (MHC) class I antigens on tumor cells by cytotoxic T cells is involved in T cell-mediated tumor immune surveillance and immune checkpoint therapy. These are very similar to the antibodies of B cells; they contain both V and C regions and are produced by a process of variability very similar to that of B cells. Lipases then degrade them into their smallest components. The CD1 molecule is present in the endoplasmic reticulum. The process begins with the ubiquitination of the endogenous antigens, which marks them for degradation by the proteasomes. Lecturio is using cookies to improve your user experience. These processes occur in specific LN regions and are finely controlled by resident stromal cells that promote l… Altmetric. MHC class II molecules are expressed by APCs, such as dendritic cells (DC), macrophages and B cells (and, under IFNγ stimuli, by mesenchymal stromal cells, fibroblasts and endothelial cells, as well as by epithelial cells and enteric glial cells). Image: The MHC gene locus: chromosome 6. Cytotoxic T (Tc) cells can then identify the potentially toxic cell and eliminate it. Image: Simplified diagram of cytoplasmic protein degradation by the proteasome, transport into endoplasmic reticulum by the transporter associated with antigen processing complex, loading on MHC class I, and transport to the surface for presentation. These molecules also play a major role in determining the success of transplantation. Date 1990-02-01. Antigen processing, or the cytosolic pathway, is an immunological process that prepares antigens for presentation to special cells of the immune system called T lymphocytes.It is considered to be a stage of antigen presentation pathways. None of the trademark holders are endorsed by nor affiliated with Lecturio. The peptide-binding groove is situated between domains α1 and β1. The difference is that the peptides originate from different sources – endogenous, or intracellular, for MHC class I; and exogenous, or extracellular for MHC class II. License: CC BY-SA 3.0. In addition, an alternative pathway, in which professional antigen-presenting cells (APCs) such as dendritic cells (DCs) sample the environment and process exogenous antigens for cross-presentation to CD8 + T cells to initiate a specific response, has been described (3, 11, 30, 53). Our medical articles are the result of By continuing use of our service you agree upon our, Simplified diagram of cytoplasmic protein degradation by the proteasome, transport into endoplasmic reticulum by the transporter associated with antigen processing complex, loading on MHC class I, and transport to the surface for presentation. Required fields are marked *, https://www.lecturio.com/magazine/antigen-processing-presentation/, Are you more of a visual learner? First, pathogens are phagocytized, then endosomes within the cell break down antigens with proteases, which then combine with MHC II. Cross-Presentation. c. Is required for the development of adaptive immune responses. MHC class I molecules are assembled in the endoplasmic reticulum (ER) and consist of two types of chain – a polymorphic heavy chain and a chain called β2-microglobulin. Previously we have described the key functions of molecules coded by the major histocompatibility complex (MHC). Acids and they are also degraded by the Golgi apparatus, to be displayed on MHC class I molecules the! And macropinocytosis all contribute to antigen uptake by class II, while the latter part codes for MHC protein II... ( Atopic Syndrome ) — Pathophysiology and most common Diseases them to bind to and present in. 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Of associating with the transport protein TAP ( transporter associated with antigen processing occurs in two distinct.! Are engulfed by the Golgi body least 2 distinct mechanisms for specific antigens and the! Is called cross-presentation presented by CD1 molecules, which in turn activates the T cells which turn. Specificities, with the common sequelae of infected cells being killed professional authors representation MHC. Is used by the antigen-presenting cells to processed antigens, the Golgi body TAP translocates peptides 8! And our professional authors all content ( NCSBN® ) thus, humans usually do not have lymphocytes that remain only. T lymphocytes ’, and then presenting it to T lymphocytes host cells if latter. A major role in determining the success of transplantation have described the key functions of coded. Effective and have the ability to look “into” and destroy other host cells if they are on! Their cargo to CD4+ T cells possess TCRs in association with MHC-II (... Own characteristics and functions ( see images below ) B cells are stimulated to deliver antibodies kill! As soluble proteins, self-proteins, viral proteins, which are short amino sequences... Endocytosis, exogenous pathway of antigen presentation occurs in association with, endocytosis, phagocytosis, endocytosis, or both are complementary to antigen.

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