James Goding; Week 10 MED1011; Pathology
Thymus creates T cells, encounter antigen and become activated to either CD8 kill cells by direct contact or CD4 help B cells to make antibodies. They also regulate many other cell types. Regulatory have CD4 and CD25 on surface. They regulate immune responses, mainly by turning them off, and may play a role in regulating autoimmunity. Cytokines are secreted by CD4 cells, act locally at short distance, cause cellular activation and modulation of cellular activity. MHC encodes proteins on surface of all nucleated cells.
Class I MHC are located on all cells, Class II are located on B cells and APCs. T cells are presented to by APCs that then causes clonal expansion. T cells cannot see naked antigen, so have to have it presented to them in the MHC groove. T cells kill virally infected cells, preventing the spread of infection. They induce apoptosis.
Dendritic cells are located in skin and around the body. They take up antigen and present it to T cells. In skin, they are called Langerhans cells. Efficient endocytosis allows capture of antigen. They are activated by bacterial products and migrate to lymph nodes. In lymph node they are less efficient at endocytosis but good at presenting antigen. Immune responses are often initiated in lymph nodes. Class I MHC 7-8aa, confined to groove, class II is 12-15aa, can spill out ends. Class I presents to killer T cells, II to helper. Class I presents what is synthesised inside the cell (viruses, transplanted organs). Loading of peptides into the groove occurs in endoplasmic reticulum. Class II presents antigen that enters cell from outside (bacterial toxins which are neutralised by antibody).
99% of cells born in the thymus die in the thymus.