Growth inhibitory effect of bovine lactoferrin on Toxoplasma gondii tachyzoites in murine macrophages: role of radical oxygen and inorganic nitrogen oxide in Toxoplasma growth-inhibitory activity.

To study the effector pathway of Toxoplasma growth-inhibitory activity induced by lactoferrin in murine macrophage, the role of reactive oxygen intermediates (O2-) and inorganic nitric oxide (NO) was examined. Production of O2- was diminished in cultures of macrophages supplemented with lactoferrin and the effect of lactoferrin was dose and time dependent. Production of NO was enhanced in cultures of macrophages supplemented with interferon-gamma, but not with lactoferrin. These findings suggest that this Toxoplasma growth-inhibitory activity induced by lactoferrin in macrophages is not mediated by O2- or NO molecules. A competitive inhibitor of the L-arginine dependent effector pathway, NG-monomethyl-L-arginine (NG MMA), virtually abolished the inhibitory effects induced by interferon-gamma. Similarly, the inhibitory activity induced by lactoferrin was also diminished in cultures supplemented with NG MMA. From these findings, it appears that the Toxoplasma growth-inhibitory activity induced by lactoferrin in macrophages may be mediated by an L-arginine-dependent effector pathway that does not involve NO production.

Divalency of the monoclonal antibody 5-1-6 is required for induction of proteinuria in rats.

A single i.v. injection of 3 mg of the F(ab')2 fragment of MoAb 5-1-6 into rats induced immediate proteinuria (128.1 +/- 80.7 mg/24 h on day 1) which lasted 1-2 days. In contrast, rats administered 10 mg of the corresponding Fab fragment did not develop abnormal proteinuria even though an equivalent dose of the intact MoAb 5-1-6 far exceeded the nephritogenic dose. The total kidney binding of 125I-Fab fragment was 209.5 +/- 34.3 micrograms/2 kidneys. This exceeded that obtained by injection of 3 mg MoAb 5-1-6 IgG1 (58.9 +/- 12.5 micrograms/2 kidneys at 1 h) and was similar to that obtained following injection of 3 mg F(ab')2 fragment (235.3 +/- 16.9 micrograms/2 kidneys). Immunofluorescence (IF) showed a linear pattern along the glomerular capillary wall at 1 h after the administration of MoAb 5-1-6 IgG1, F(ab')2 or Fab fragment. On day 5, fine to coarse granules were observed scattered in F(ab')2-injected rat glomeruli, whereas granules were densely localized in Fab-injected rat glomeruli. Complement-depleted rats injected with 3 mg of MoAb 5-1-6 IgG1 developed proteinuria with the same time course as non-depleted rats. This observation, together with the ability of F(ab')2 to induce proteinuria, indicates that proteinuria induced by MoAb 5-1-6 is complement-independent. This study suggests that MoAb 5-1-6-induced proteinuria is initiated by cross-linking of the epitopes by divalent MoAb 5-1-6 and is independent of complement activity.