Mechanisms of hypersensitivity: cellular interactions. Basophil arrival and function in tissue hypersensitivity reactions.

Bone marrow-derived blood basophils are recruited into the tissues by immuno mechanisms in a variety of delayed time-course hypersensitivity responses. In the skin these are called cutaneous basophil hypersensitivity (CBH) reactions. In guinea pigs, it is now established that the elicitation of CBH is dependent on T cell- and/or (antibody)-triggered mechanisms. Both are subject to modulation. T cell-mediated CBH seems to be suppressed in basophil-poor tuberculin-type reactions. B cells mediate CBH via antibody of IgG1 isotype through mechanisms that involve Fc receptors, which can be competitively blocked. After basophils arrive at a CBH reaction they can be triggered by antigen to immediately release mediators such as histamine. Thus, one consequence of the arrival and accumulation of basophils at delayed hypersensitivity reactions is to augment the anaphylactic potential of a given tissue site. In reactions to parasites, release of mediators by tissue basophils seems to aid in the expulsion of these multicellular organisms, In addition, histamine released by recruited basophils, or by locally resident mast cells, may modulate some delayed reactions through stimulation of histamine-2 receptors on cells such as T lymphocytes. In mice, mast cell release of serotonin and subsequent stimulation of the local vasculature seems to be required to allow diapedesis and tissue accumulation of various bone marrow-derived accessory leukocytes in delayed-type hypersensitivity responses. Thus, basophils and mast cells, and their release of mediators such as vasoactive amines, are involved in the onset, development, and function of various tissue hypersensitivity responses.