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Humoral Immunostimulation

VI. Increased Calcium Uptake by Cells Treated with Antibody and Complement¹

Departments of Pediatrics and Medicine, Washington University School of Medicine, St. Louis, Missouri 63110

Abstract

When L cells were treated with anti-L cell antibody in medium depleted of complement, rapid increases in calcium uptake were obtained over a wide range of antiserum concentrations. Concomitant cell growth and viability studies demonstrated that stimulation of cell growth occurred at higher dilutions of antiserum whereas cytotoxicity occurred at lower dilutions. The stimulatory and toxic effects of antibody on cell growth were potentiated by complement as was the enhancement in calcium uptake. Sera deficient in C1R, C2,4D, C4, C3–C9 did not increase the calcium uptake response to antibody whereas augmentation did occur with C6-deficient serum. A specific role for complement was further indicated by the ability of purified complement components to restore the response to complement in complement-deficient sera. C3 with C3–C9 deficient serum, but not C2, C5, and C6 with C3–C9 deficient serum restored augmentation effects. Taken together with the results of previous studies it is apparent that complement augments both calcium and nucleoside uptake and that the effect is primarily via the classical complement pathway through C3.

Substrate saturation studies demonstrated that antibody activated the facilitated diffusion of calcium altering the V_max but not the K_m of transport whereas adddition of complement altered both the V_max and K_m. These findings suggest that one of the early effects of enhancing antibody upon tumor cell metabolism in vitro is to stimulate uptake of calcium. In view of the suspected role of Ca⁺⁺ in cell proliferation the increase in cell-associated calcium may be important in the subsequent proliferative response.

Footnotes

¹ This work was supported in part by a Research Scholar Award from the Cystic Fibrosis Foundation to W.T.S., Grants 5R01-Ca 12626 and 1R-1-Ca 16391 from the National Institutes of Health, and by a Grant from the American Cancer Society (IM-54).

² Please address correspondence to: William T. Shearer, M.D., Ph.D., St. Louis Children's Hospital, 500 South Kingshighway, St. Louis, Missouri 63110.