1566 Human Neutrophil - Immobilizing Factor

The capacity of humoral factors to influence polymorphonuelear leukocyte function has been recognized by in vitro studies. Neutrophil phagocytosis is enhanced by the presence of a fragment of the third component of complement, C3b, on a target cell or complex (1). Neutrophils respond chemotacticallv in vitro to by-products of the complement reaction sequence such as the cleavage product of the fifth complement component, CSa, or the trimolecular complex of the fifth, sixth, and seventh components of complement, C567, and to components of the kinin-generating system such as kallikrein (2-4). The inhibitor of the activated first component of complement (CIINH) blocks the neutrophil response to kallikrein. 1 Other factors which suppress chemotaxis in vitro are found in the sera of some patients (5-7). These factors have not been isolated, and in most instances it has not been definitively determined whether such inhibitors function by blocking the stimulus or by affecting the neutrophils directly. In addition, as chemotactic principles can deactivate their target cells, specific inhibitors must be separated from contaminating chemotactic activity.