Cell-Mediated Immune Responses in Neonates

Abstract

Cell-mediated immune (CMI) responses are mediated by T cells. T-cell subsets, such as Th1 and Th2, exhibit various functions. CD4 Th1 cells are the effectors of delayed-type hypersensitivity reactions, producing cytokines such as IFN-γ, which activates macrophage to kill obligatory intracellular pathogens, and interleukin (IL)-2, which promotes the growth of CD8 T cells. Th1 cells also promote class switching of IgM to IgG2. Th2 cells secrete cytokines to promote the B-cell activation and class switching of IgM to IgG1 and IgE. The CD8 cytotoxic T cells (CTLs) lyse cells infected with microbes (viruses, intracellular bacteria, and parasites) as well as cells expressing tumor-associated antigens. Therefore, CMI responses play an important role in immune defense reactions.