Co-chemotactic effect of Gc-globulin (vitamin D binding protein) for C5a. Transient conversion into an active co-chemotaxin by neutrophils.
Gc-globulin (vitamin D binding protein) has been shown to augment significantly the leukocyte chemotactic activity of the activated C peptides C5a and C5adesArg (i.e., the co-chemotactic effect). However, the mechanism of chemotaxis enhancement is not known. To investigate the role that the neutrophil plays in this process, cells were co-incubated with Gc-globulin for up to 45 min and washed, and their subsequent chemotactic response to a suboptimal concentration of C5a alone was measured during a 30-min assay. The generation of co-chemotactic activity during the preincubation period was time dependent, showed minimal activity for the first 10 min and a steep rise from 10 to 20 min, and was maximal and stable at 30 min. The binding of radiolabeled Gc-globulin by neutrophils at 37 degrees C mirrored this time-dependent generation of C5a co-chemotactic activity, with stable cellular levels achieved between 30 and 45 min at 36 +/- 4 fmol (2 +/- 0.1 ng)/10(6) cells. The binding of radiolabeled Gc-globulin and the generation of co-chemotactic activity were dependent upon physiologic temperatures (37 degrees C) and levels of Ca2+ (1.3 mM) and Mg2+ (0.8 mM), and were inhibited by an Ab to Gc-globulin. Finally, the C5a co-chemotactic activity of Gc-globulin would decay rapidly if neutrophils were washed and then incubated a second time at 37 degrees C before chemotaxis to C5a. These results demonstrate that neutrophils bind exogenous Gc-globulin and generate C5a co-chemotactic activity in a time-, temperature-, and divalent cation-dependent manner. Moreover, this activity is transient if neutrophils lack a continuous supply of Gc-globulin.
Kew
R R
RR
Department of Pathology, State University of New York at Stony Brook 11794, USA.
Fisher
J A
JA
Webster
R O
RO
D002118:Calcium / Q000494:pharmacology; D002630:Chemotactic Factors / Q000378:metabolism*; D002634:Chemotaxis, Leukocyte / Q000187:drug effects; D015936:Complement C5a / Q000187:drug effects*; D006801:Humans; D009504:Neutrophils / Q000378:metabolism*; D013696:Temperature; D013997:Time Factors; D014809:Vitamin D-Binding Protein / Q000378:metabolism / Q000494:pharmacology*
D002630:Chemotactic Factors; D014809:Vitamin D-Binding Protein; D015936:Complement C5a; D002118:Calcium