Adaptive Immune System

The specialists.

HLA/MHC

Name tag system – indicates to the lymphocytes “please have a look at this particle, and see if its ok…..”

Like presenting wares at a market for the diverse T cells to look through

Class I presents particles for any cell with an internal problem to allow T-helper and T-cytotoxic cells to consider eg viral infection, cancer . The T helper cell activates the B cells to produce antibody, and activates the cytotoxic T cells to kill the cells.

Class II presents external particles, such as debris or invaders which has been picked up by surveillance “antigen presenting cells”, such as DCs or macrophages. They present to the T cells which respond by producing cytokines which activate inflammation and B cells.

There are two types of T cells:

CD8+ cytotoxic T cells which act by recognising HLA Class I presentation of antigen and kill the cell

CD4+ helper T cells, which orchestrate the whole adaptive immune system. After antigen presentation, they release cytokines, which influence other cells. The cytokines they produce determines the type of reaction that results (ie which cells are activated and recruited, and which antibodies the B cells produce). The types of cytokines release can be divided into two groups, Th1 and Th2….the two main subgroups of CD4+ T helper cells.

B cells recognise antigens via the antibodies on their surface which act as receptors

They internalise these antigens, and then present them via HLA Class II to the lymphocytes (once again, “please have a look at this particle, and see if its ok…..”). If the T cells responds with activation, it will release cytokines, which enable the B cell to mature and produce more specific antibodies via somatic hypermutation

1. Activate complementADCC – Antibody Dependent Cellular Cytotoxicity (NK cells and macrophages)
2. Neutralisation of toxins (eg the gut)
3. Opsonisation to enhance phagocytosis
4. Mucosa Protection
5. Agglutination – form immune complexed which can then be cleared by red blood cells

Category: Pathology Notes