Notes
Effector Cell Functions
Cytotoxic T cells directly kill pathogen-bearing cells via the following steps:
- The T cell recognizes the MHC I – antigen complex.
- Docking brings the two cell membranes in close association.
- The T cell releases perforins, which form a pore in the infected cell's membrane.
- The cytotoxic cell releases granzymes, which move through the pore and trigger apoptosis of the infected cell.
Helper T cells, the products of activated CD4+ cells, have multiple roles in both innate and adaptive responses:
- They amplify the innate response via cytokine release and recruitment of neutrophils and macrophages.
- They activate B cells, which mediate the humoral arm of the adaptive immune response.
- They activate cytotoxic T cells, in part by upregulating the expression of co-stimulatory molecules on dendritic cells.
- Superantigens, such as Staphylococcus bacteria, are super potent activators of CD4+ cells.
4 subsets of Helper T cells:
- Th1: develop under the influence of interferon-gamma and IL-12.
Anti-viral activity, macrophage activation, and induce cytotoxic T cell differentiation; when unregulated, they are associated with autoimmune diseases.
This subset produces IL-2 and interferon-gamma.
- Th2: develop under the influence of IL-4.
This subset is particularly important in defense against worms and in mobilization of eosinophils; they are associated with allergies and asthma.
They produce IL-4, IL-5, and Il-13.
- Th17: develop under influence of Tissue growth factor-beta, IL-6, IL-1, and IL-23.
This subset recruit neutrophils and monocytes.
They are also associated with autoimmune disease.
They produce IL-17 and IL-22.
- Follicular helper T cells: differentiation is thought to require interaction with B cells.
Follicular helper T cells promote the humoral immune response and produce IL-21.