Adaptive Immunity to Extracellular Bacteria

Cancer Immun System

Humoral immunity is a major protective immune response against extracellular bacteria, and it functions to block infection, to eliminate the microbes, and to neutralize their toxins (Fig. 15-1A). Antibody responses against extracellular bacteria are directed against cell wall antigens and secreted and cell-associated toxins, which may be polysaccharides or proteins. The polysaccharides are prototypic thymus-independent antigens, and humoral immunity is the principal mechanism of defense against...

Differentiation of CD4 T Cells into TH1 TH2 and Th17 Effector Cells

Th1 Effecting Macrophage

Effector cells of the CD4 lineage are characterized by their ability to express surface molecules and to secrete cytokines that activate other cells B lymphocytes, macrophages, and dendritic cells . Whereas naive CD4 T cells produce mostly IL-2 on activation, effector CD4 T cells are capable of producing a large number and variety of cytokines that have diverse biologic activities. There are three distinct subsets of CD4 T cells, called Th1, Th2, and TH17, that function in host defense against...

Contraction homeostasis

Stages The Immune Response

FIGURE 1-6 Phases of adaptive immune responses. Adaptive immune responses consist of distinct phases, the first three being the recognition of antigen, the activation of lymphocytes, and the elimination of antigen (the effector phase). The response contracts (declines) as antigen-stimulated lymphocytes die by apoptosis, restoring homeostasis, and the antigen-specific cells that survive are responsible for memory. The duration of each phase may vary in different immune responses. The y-axis...