One of the most interesting developments in biomedical science during the past few decades has been elucidation of mechanisms mediating innate immunity. One set of innate immune mechanisms is humoral, such as complement activation. Another set comprises pattern recognition receptors such as toll-like receptors, which induce the production of interferons and other cytokines increasing resistance of cells such as monocytes to infections. Cytokines produced during innate immune responses are among the activators of adaptive immune responses. Antibodies exert additive or synergistic effects with mechanisms of innate immunity. Unstable HbS clusters Band-3, a major integral red cell protein; antibodies recognize these clusters and accelerate their removal by phagocytic cells. Clustered Band 3 proteins with attached antibodies activate complement, and complement C3 fragments are opsonins recognized by the CR1 complement receptor on phagocytic cells.