Patricia J. Baker

Complement membrane attack complex stimulates production of reactive oxygen metabolites by cultured rat mesangial cells.

To explore possible mechanisms by which complement membrane attack complexes (MAC) that are deposited in the glomerular mesangium might be pathogenic, we stimulated rat glomerular mesangial cells grown in vitro with nascent MACs formed from the purified human complement components C5b6 and normal human serum and measured production of superoxide ion (O2-) and hydrogen peroxide (H2O2). Mesangial cells incubated with C5b6 + serum, which results in cell membrane interaction with the MAC, produce 0.9 +/- 0.15 nmol O2-/10(5) cells per 30 min, which was significantly greater than the amount produced by cells incubated with C5b6 alone, serum alone, or decayed MACs that can no longer interact with the cell membrane (0.3 +/- 0.2, 0.4 +/- 0.1, 0.3 +/- 0.2 nmol O2-/10(5) cells per 30 min, respectively; P less than 0.02). Production of O2- after stimulation with MACs increased during the first 20 min of incubation but then plateaued. Cells exposed to decayed MACs produced small amounts of O2-, which did not increase from 20 to 60 min. Production of H2O2 was also observed after stimulation with MACs, and continued to increase during 60 min of incubation (1.22 +/- 0.16 nmol H2O2/10(5) cells per 60 min), whereas H2O2 production could not be detected after exposure to decayed MACs. Cell viability was not adversely affected by exposure to nascent MACs as determined by trypan blue exclusion or chromium-51 release. These results demonstrate that glomerular mesangial cell membrane interaction with the MAC stimulates the production of the toxic oxygen metabolites O- and H2O2. Activation of the terminal complement pathway by mesangial immune deposits in vivo might lead to tissue injury by stimulation of local production of toxic oxygen-free radicals.

Platelets mediate neutrophil-dependent immune complex nephritis in the rat.

Neutrophils and platelets are frequently present in glomeruli in immune glomerulonephritis (GN). No role for the platelet in acute neutrophil-mediated renal injury has been defined. We investigated a neutrophil-mediated model of subendothelial immune complex GN in the rat. Rats were platelet-depleted (mean platelet less than 10,000/microliter) with goat anti-platelet IgG before induction of GN by the renal artery perfusion of concanavalin A followed by anti-concanavalin A IgG. Platelet-depletion resulted in a significant reduction in albuminuria (7 +/- 2 vs. 55 +/- 10 mg/24 h) and fractional albumin excretion (0.045 +/- 0.01 vs. 0.410 +/- 0.09) compared with controls. The decrease in albuminuria was not due to differences in blood or glomerular neutrophil counts, complement, renal function, or glomerular antibody binding. Platelet-depleted rats had equivalent subendothelial deposits and glomerular endothelial cell injury but had minimal platelet infiltrates and fibrin deposition compared with controls. These studies demonstrate a role for platelets in mediating acute neutrophil-induced glomerular injury and proteinuria in this model of GN.

MECHANISMS OF TUMOR HOMOGRAFT REJECTION: THE BEHAVIOR OF SARCOMA I ASCITES TUMOR IN THE A/JAX AND THE C57BL/6K MOUSE*

The respective roles that classical humoral antibodies and hypothetical “cellassociated” antibodies may play in tumor homograft rejection and the mechanisms by which they act remain major unsolved problems in homograft immunity. Whereas classical humoral antibodies to tumor homografts are commonly produced, their participation in tumor rejection has been clearly demonstrated only in a limited number of tumor-host combinations. Tumors derived from cells of the lymphoid series appear to be particularly susceptible to in vivo destruction by humoral antibody. Excellent discussions of the evidence bearing on the problem of the mechanisms of tumor homograft rejection have been presented recently by Gorer,’ Amos: and Snell and co-~orkers .~ The purpose of the present investigation is to gain further information about the mechanisms by which cell-associated antibody factor of immune host cells may accomplish the destruction of tumor cell homografts. The system, Sarcoma I (Sa I) in the C57BL/6K mouse, was chosen because it is one in which homograft rejection appears to depend solely on cell-associated antibody. Indeed, in this system classical humoral antibody exerts a suppressive rather than an augmentative effect on tumor rejection and induces an “immunological enhancement” of tumor growth rather than i m m ~ n i t y . ~ Sarcoma I originated in 1947 in a mouse of the Strong A strain that had been treated with dibenzanthracene. The tumor grows progressively in the A/ Jax subline of the Strong A mouse and kills 100 per cent of the animals. In contrast, mice of the resistant C57BL/6K strain, given a standard dose of 30 million ascites tumor cells by the intraperitoneal route, reject the tumor in essentially 100 per cent of the cases. The tumor shows unrestricted growth in the animals until the 6th or 7th day, when rejection begins. Rejection is largely completed by the 8th day, and the animals remain immune to rechallenge for weeks thereafter. Since our preliminary attempts failed to demonstrate that Sa I cells are destroyed by reaction in vitru with immune cells, attention was centered on in vizw studies of interaction between immune host cells and tumor cells. If the rejection of Sa I by the C57BL/6K mouse results from contact of immune