ABSTRACT
T-helper cells are an absolute requirement for immune responses to protein antigens in general, and for helping B cells to make the different classes of antibodies. The type of response that develops is, in some instances, determined by the nature of the antigen and its mode of entry, as well as the effect of regulatory CD4+ T-helper subsets, Th1 and Th2, and their cytokine products (Section F5). The pro-inflammatory cytokines IL-2, TNFα and IFNγ produced by Th1 cells are important for killing of intracellular microbes and 164the generation of T-cytotoxic cells, as well as the development of IgG antibodies capable of mediating phagocytosis of extracellular microbes. In contrast, the anti-inflammatory Th2 cytokines IL-4, IL-10, and IL-13 are important for B-cell proliferation and differentiation and immunoglobulin class switch to IgA and IgE as well as the IgG2 response to the polysaccharide antigens associated with encapsulated bacteria such as Pneumococcus. Th2 cytokines are also important in helping to eradicate parasitic infections as they lead to the production of IgE and the recruitment of eosinophils, which have powerful anti-parasitic functions (Section H2).
