Stimulation of human neutrophilic granulocyte chemotaxis by monoclonal antibodies

Two mouse monoclonal antibodies, L12.2 and S5.22, were developed that are specific for human neutrophilic granulocytes and produce a twofold to threefold stimulation of n-formyl-methionine-leucyl-phenylalanine (FMLP)-induced chemotaxis. Stimulation of chemotaxis by the antibodies is specific for FMLP and is concentration dependent. L12.2 appears to be more potent in stimulating chemotaxis and is isotypically distinct from S5.22. In addition, although L12.2 reacts only with mature peripheral blood granulocytes, S5.22 reacts with leukemic cells of both myeloid and monocytic origin and with immature granulocyte precursor cells. This suggests that L12.2 interacts with an antigen that appears late in the differentiation pathway, whereas S5.22 binds to an antigen that is present throughout the myeloid lineage. By means of the under-agarose and Boyden chamber techniques, L12.2, but not S5.22, by itself was also found to be a potent granulocyte chemoattractant. Cells in a gradient of L12.2 display polarized and oriented morphology. L12.2 alone, but not S5.22, also stimulates granulocyte phagocytosis and induces superoxide anion production. Neither L12.2 nor S5.22 affected the release of myeloperoxidase or lysozyme from granulocytes either alone or in combination with FMLP, C5a, or the tumor promoter, 12-O-tetradecanoyl-phorbol-13-acetate (TPA). These results suggest that L12.2 interacts with a single antigenic determinant on granulocytes that is involved in chemotaxis, phagocytosis, and superoxide anion release.