what is antigen presenting cell

 

Antigen presenting cell

Introduction

Individual is protected from different type of pathogen with the help of immune system. with the help of confocal microscope, we observe mechanism of immune system.

Antigen is defined as cell that is specialized cell that is responsible to stimulate to immune system to fight against disease. There are two types of antigen. Foreign antigen is produced from outside body like infection of virus, bacteria and second type are autoantigen. Antigen presentation cell has two subset professional antigen presenting cell and amateur antigen presenting cell. Macrophage monocyte dendritic cell and b cell are professional antigen presenting cell. Amateur antigen present cell like glial cell pancreatic beta cell keratinocyte cell and thyroid gland act only in special condition. First, we discuss antigen presenting cell

Antigen presenting cell

Monocyte and microphage

Foreign particles engulf by monocyte and microphages. Microphage cell that presents in tissue and monocyte circulate with in blood. Microphages are present in bone, connective tissue, and brain. Kupffer cell are microphage that present in liver cell. Adaptive and innate immunity is controlled by microphages. PAMP, Toll-like, scavenger, and mannose receptors bind with antigen to activate microphages

Dendritic cell

Dendritic cell was described by Steinmann 1973. These are professional antigen cell that produce in bone marrow and part of lymphoid and nonlymphoid tissue. Myeloid stem cell produces two type of dendritic population. Follicular dendritic cell produces when one population migrate toward lymph node. Second population present in non-lymph node and then change in to interstitial dendritic cell. Dendritic cells are suitable for specific antigen presentation These cell highly concentrated at place where microbe enter. Presentation of T cell is processed by dendritic cell and microbe is captured by dendritic cell. Dendritic cells have ability to move in tissue so they stimulate lymph node.

Follicular dendritic cell

Lymph node germinal follicle are responsible in production of follicular dendritic cell. Follicular dendritic cell perform function to activate b cell and main immunological memory. Only FDCs dendritic cell that does not participate in antigen presentation of T cell. FDCs cell produce cytokines that is responsible for activation of B cell in plasma.

Interstitial Dendritic cell

Except brain and eye interstitial cell present in all tissue. The function of these cell to detect foreign particle in body. IDC present in skin in large quantity, skin contain 25% of Langerhans cell and 2- 3 % skin cell.  Suprabasilar epidermis is a place where immature Langerhans cell present and identified by cytoplasmic birbeck granule when class 1 class 2 CD +4 and other receptor are expressed in response of pathogen.

Plasmacytoid dendritic cell

These cell is like antibodies that secreted from plasma cell and it is belief that production of these cell in lymphoid progenitor. PDCs are present in lymph node like spleen, tonsil, and blood. These cell activated against viral infection. When virus attack DNA of viruses is capture by toll like receptors 7 and 9. When viral DNA is captured PDCs activate alpha bd beta interferon. These interferon do not allow viral cell to attack on other uninfectious cell.

B cell

T cell is presented by B cell. B cell has specific antigen receptor that bind with antigen and then modified into antibodies. Cross linking of BCR include antigen which is breakdown in cytoplasm and presentation of T cell in context to class 2. B cell is less concentrated.  For presentation of antigen B cell concentration is 100 to 10000 time less concentrated than macrophage for antigen presentation.

Presentation of exogenic antigen

 Exogenic antigen is breakdown on the path of endocyte and fill up on class MHC2 molecule. ClassMHC 2 molecule perform their mechanism in different way with macrophage and B cell. Using different receptor like PAMPs and antibodies dendritic cell bound with antigen. Phagocytic cell ingest opsonizes bacteria and antigen. Pseudopodia is formed by invagination of membrane during re arrangement of cytokinin. Pseudopodia surround material and ingest them; these material change in internal vacuole. Foreign particle is engulfed by B cell using receptor mediated response. Clathrin membrane is area where localization of B cell receptor take place. When receptor bind with clathrin it helps calthrin to move inward membrane and make vesical.                              

Process of recycle of clathrin completed after that B receptor express on surface of cell and membrane bounded vesical change into vacuole. Phagosome is name of vacuole in microphage and B cell. Phagosome combined with lysozyme that has hydrolytic enzyme that remove material from phagosome and phagosome called phagolysosome.

Dendritic cell and cancer vaccination

Tumor cells are not actively participated in immunity as HLA move downward and antigen of tumor cell do not present to T cell. Immunity against tumor cell is increased by using cross priming vaccine. Tumor cell exerted from patient and then purified. Tumor cell and dendritic cell combine in laboratory and heat up for several day. Complete tumor cell is engulfed by dendritic cell and suitable presentation of class 2 molecule. DCs in patient produce action in responses of tumor cell. Vaccine is produced against tumor according to this concept. cancer is treated by using dendritic cell vaccine.

MHC 1 antigen presentation

MHC 1 cell are mostly present in nucleated cell. MHC1 cell is composed of heterodimer of different kind of alpha chain that coupled noncovalently with b-2 macroglobulin. It is nonpolymorphic. Alpha chain is composed of three domain. Plasma membrane is crossed by alpha 3butalph 2 and alpha 1 is responsible for antigen bonding cell. MHC1 is bounded with peptide that are 8-10 amino acid in length and peptide anchor on MHC 1 molecule with the help of amino acid that are present on specific position.

Endoplasmic reticulum produce MHC 1 molecule ‘s peptide binding site. cytosol is responsible for production of all type of protein. Proteosome are catalytic enzyme that degrade protein small peptide.

Proteome composed of 28 subunits that are cylindrical structure and contain 4 ring and each ring has seven subunit. Innate immunity release IFNs that is responsible in production of three type of proteosome subunits when viral infection take place. Proteosome are produces peptides that bind with MHC molecule when inflammation occur.

MHC class II presentation

APCs, such as dendritic cells (DC), B cell and microphages express MHCII molecule. Protein change into peptide that form binding with MHCII molecule. Alpha and beta chain are part of MHCII molecule, combine in endoplasmic reticulum and invariant chain stabile it. Golgi apparatuses transport invariant chain and MHCII molecule into different compartment these compartment called Ii and MHCII compartment. Proteases cathepsin L and cathepsin S has acidic pH, due to acidic pH these protease activate and digest it invariant chain

Pathway of antigen presentation

Two pathway is used by immune system to remove extracellular and intracellular antigen. Cytosol pathway is responsible for the processing of endogenous antigen and present on membrane. endocytic pathway is path that processed exogenic antigen and present it on membrane with molecule of MHCII.

Two scientist Morrison and Braciale perform experiment to show that presentation of peptide bond is done by MHCI and MHCII molecule Two clone of cytotoxin T cell   is used in research, molecule of class MHCI make association with influenza hemagglutinin is recognized by one type of Tc cell. Same antigen that makes association with MHCII molecule that is recognized by atypic TC line cell. Expression of both MHCI and MHC II molecule by target cell and these target cells heated these molecule with infectious influenza virus or with those virus that are inactivated with the help of UV radiation (non-activated viruses have antigen but they loss replication ability). Target cells are also heated with class I and II restricted Tc cell for the determination of lysis of target cells lysis Class I and II restricted Tc cell were heated together. In result Tc cells of class II molecule provide response against target cell which are treated with infectious or non-infectious. The class I restricted cells provide response against those target cells which were treated with infectious virus. Using emetine production of viral protein stop when class I restricted cells treated with viral infection that cause stimulation of class II restricted cell but no stimulation produces in class I restricted cells. When chloroquine using in experiment endocytic process pathway has been blocked by drug it stimulates class I restricted cell. These experiment show that exogenic antigen associated with class MHCII molecule and endogenic antigen associated with MHCII molecule.

Antigen presenting cell 

 Monocyte macrophages and T lymphocytes antigen presenting cell