Immunology

Adaptive immunity

T cells and B cells recognize antigen differently

• B cells (antibody cells) recognize antigen alone

• B cells recognize intact antigen

• T cells recognize antigen + MHC

• T cells recognized processes antigen

T lymphocytes

• Mature in the thymus• T cells recognize only a small part of the

antigen (B cells recognize intact antigen)• T cells recognize antigen only when it is

bound with MHC– Major histocompatibility complex: important in

tissue transplants

• Then the T cells proliferate and differentiate into memory and effector T cells

Antigen is presented to the T cells after it has been processed by the antigen presenting cell

Antigen presenting cells

• Takes in foreign particles - antigens

• Breaks them down

• Reexpresses fragments on the surface of their cells in combination with its own self proteins – MHC

Two different types of T cells

• Helper T cells– Contain CD4 glycoprotein on their surface– Recognize antigen bound to class II MHC– Initiate the proliferation of lymphocytes– Once activated, secretes cytokines (IL-2) that

activate B cells, cytotoxic T cells and macrophages

Two different types of T cells

• Cytotoxic T cells– Have CD8 on their surface

– Recognize antigen in the context of MHC class I

– Don’t release cytokines

– Directly kill cells

– Kill virally infected cells and tumor cells

– Perforin produced – makes holes in the infected cell membrane

Cytotoxic T cells

Helper and cytotoxic T cells

Helper and cytotoxic T cells

Summary of different cells

CD8 cells recognize antigen in the context of MHC class I

• Antigen is processed/broken down before it is presented to the T cell (antigen presenting cells): proteosome

• Internal foreign antigen

• It must bind with MHC and then it is recognized by the T cell receptor

• MHC Class I = CD8 = cytotoxic T cells

CD4 cells recognize antigen in the context of MHC class II

• Antigen is processed/broken down before it is presented to the T cell

• External foreign protein

• It must bind with MHC and then it is recognized by the T cell receptor

• MHC Class II = CD4 = helper T cells

Summary of different pathways

Processing pathways animations

• http://www.bio.davidson.edu/courses/Immunology/Flash/MHCI.html;

http://www-ermm.cbcu.cam.ac.uk/smc/swf002smc.htm