Lack of specificity of brain gangliosides in the modulation of lymphocyte activation.

A potential role for glycolipid gangliosides to act as immunomodulating agents has been suggested. Most studies have employed brain gangliosides. We have systematically investigated highly purified murine brain gangliosides for their ability to modulate lymphocyte activation. All sialic acid classes of ganglioside inhibited lipopolysaccharide (LPS)-induced antibody secretion and all polysialated gangliosides inhibited LPS-induced DNA synthesis. Monosialated gangliosides had no effect on DNA synthesis induced by LPS. 8-BrcGMP-induced DNA synthesis was also inhibited, suggesting that a negative signal was delivered to B lymphocytes by co-cultivation with exogenous gangliosides. The lack of specificity with respect to sialic acid class observed in these studies suggests that further investigation of an immunomodulatory role for gangliosides focus on endogenous lymphocyte gangliosides.

Lymphocyte mediation of lipopolysaccharide-stimulated macrophage metabolism.

LPS activation of murine macrophage metabolism and arginase production may be mediated by products of B lymphocytes. Splenic nonadherent cells, containing both B and T lymphocytes, splenic T cells, and thymocytes all stimulated macrophage glucose metabolism in co-culture. Supernatants derived from preculturing each of these cells in the absence of serum or other exogenous stimulant were also active in enhancing macrophage glucose utilization. When lipopolysaccharides were used to stimulate the lymphocyte populations, only the B lymphocyte containing NASC and purified B cells exhibited increased stimulatory activity. Thus, it appears that LPS does not directly activate T cells to produce macrophage-activating factors. The converse does not appear to be true, however, because LPS-stimulated macrophages enabled thymocytes to exhibit an enhanced ability to stimulate further macrophage glucose utilization. The active supernatant from NASC was heat resistant and remains to be chemically defined. These experiments clearly demonstrate that LPS-induced macrophage activation may be mediated by the products of lymphocytes, and that products derived from nonactivated lymphocytes are capable of stimulating macrophage metabolism and arginase production.

Stimulation of peritoneal cell arginase by bacterial lipopolysaccharides.

The conditions under which bacterial endotoxins stimulate arginase production in mouse peritoneal macrophages have been defined. Both lipid-A and lipid-A-associated protein are potent activators. Fetal calf serum and normal mouse serum enhance macrophage arginase levels in the presence and absence of lipopolysaccharide (LPS). LPS in the amount of 10(-1) microgram/ml represents a maximal stimulus for macrophage arginase production and release. Thioglycollate-elicited peritoneal cells have increased arginase activity, compared with resident cells. This activity can be stimulated further by the addition of LPS. Arginase levels may alter the outcome of in vitro immunologic processes by depleting arginine and may also serve as a useful indicator of the state of activation of macrophages.

Stimulation of Ca2+-dependent neurotransmitter release and presynaptic nerve terminal protein phosphorylation by calmodulin and a calmodulin-like protein isolated from synaptic vesicles.

Synaptic vesicles have a Ca(2+)-dependent protein kinase system that may play a role in mediating Ca(2+)-stimulated neurotransmitter release and vesicle function. Calcium's ability to initiate norepinephrine release and protein phosphorylation in synaptic vesicle preparations was shown to be stimulated by the presence of an endogenous heat-stable vesicle protein fraction. The heat stability and characteristics of this endogenous vesicle fraction were similar to those of calmodulin (Ca(2+)-dependent regular protein) isolated from rat and bovine brain. Calmodulin, like endogenous heat-stable vesicle factor, restored calcium's ability to stimulate vesicle neurotransmitter release and protein kinase activity. Calmodulin-like vesicle protein and purified calmodulin were also equally effective in stimulating cyclic nucleotide-dependent phosphodiesterase, further indicating that these two proteins are functionally equivalent. Depolarization-dependent Ca(2+) uptake in intact synaptosomes simultaneously stimulated release of neurotransmitter and phosphorylation of particular synaptic vesicle proteins that were shown in the isolated vesicle preparation to be dependent on Ca(2+) and calmodulin. The results suggest that calcium's effects on neurotransmitter release and presynaptic nerve terminal protein phosphorylation may be mediated by endogenous calmodulin-like proteins.