Immunofluorescence studies showed that properdin (P) and factor B bind to C3-C3b receptor bearing human lymphoblastoid cells (Raji, Daudi) and B type human peripheral lymphocytes (HPL). P bound to Raji cells first incubated with normal human serum (NHS). EDTA, but not EGTA, halted the binding of P to cells incubated with NHS. However, fixation of P to Raji cells, after incubation with NHS first reacted with inulin, was independent of Ca++ and -g++ ions. Fixation of P to Raji cells depended on the presence of C3 or C3b and occurred in the absence of factor D and factor B. Binding of P to B type HPL was detectable only after incubation of these cells with NHS first reacted with inulin; under these conditions binding of P to Raji cells was also greatly enhanced. With both Raji cells and HPL, factor B was detectable on cell surfaces only after incubation of these cells with NHS first reacted with activators of the P system. Binding of factor B to cells required the presence of C3b and binding or stabilization of cell bound factor B necessitated the presence of activated P. P and factor B were detectable only on cultured cells having C3-C3b receptors. However, incubation of NHS with all lymphoblastoid cell lines studied resulted in activation of P and cleavage of factor B. Binding of P and factor B to cells may follow one of three sequences; (a) activated P in fluid phase combines with C3, factor D, and factor B, and the whole complex fixes to cellular C3-C3b receptors via its C3 moiety; (b) C3b generated in fluid phase combines with P, C3, factor D, and factor B and binds to C3-C3b receptors; or (c) C3 or C3b first binds onto the C3-C3b receptors and thereafter interacts with P, factor D, And factor B. Binding of components of the P system to cells or other particles may relate to such biological phenomena as lysis, phagocytosis, proliferation, attraction of other cell types, and alteration of responsiveness to external stimuli.

This content is only available as a PDF.