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M L Francis

Publications and source records attributed to M L Francis.

6 recordsLinked to original sources
PubMed1992

Cyclic AMP-independent effects of cholera toxin on B cell activation. II. Binding of ganglioside GM1 induces B cell activation.

Although the physiologic function of gangliosides is unknown, evidence suggests they play a role in the regulation of cell growth. The binding of ganglioside GM1 by recombinant B subunit of cholera toxin (rCT-B) inhibited mitogen-stimulated B cell proliferation without elevating intracellular cAMP. CT-B paradoxically enhanced the expression of MHC class II (Ia) molecules and minor lymphocyte-stimulating determinants without altering the expression of some other immunologically relevant B cell surface Ag. Increased expression of Ia was not detected until 4 h after stimulation, kinetics similar to those seen when B cells are stimulated with anti-Ig antibody or IL-4, suggesting that the enhancement was not the result of redistribution of existing cell surface markers but rather the result of a new metabolic event. Both the inhibitory and stimulatory effects of CT-B could be blocked by incubation of CT-B with ganglioside GM1. Furthermore, enhancement of the CT-B-mediated effect was seen when additional ganglioside GM1 was incorporated into the B cell membrane. rCT-B with a mutation that interfered with its binding to ganglioside GM1 did not enhance Ia expression. Taken together, these results indicate that the observed effects of CT-B were most likely mediated through the binding of cell surface ganglioside GM1. CT-B-mediated stimulation of Ia expression provides a potential explanation for the previously described ability of CT-B to act as an immunoadjuvant. These results suggest that the binding of ganglioside GM1 has multiple B cell growth-regulating effects.

Animals↗
PubMed1992

Interferons in the persistence, pathogenesis, and treatment of HIV infection.

Interferon (IFN) plays an important role in the treatment and pathogenesis of HIV disease. Recent studies show beneficial effects of IFN alpha in the treatment of HIV-associated Kaposi's Sarcoma and early HIV-infection. Moreover, cell culture studies support these beneficial effects. HIV infection of monocytes is blocked by IFN alpha administered at the time of viral challenge. The IFN alpha-treated cells show no evidence of HIV infection. Viral gene products produced in monocytes infected with HIV then treated with IFN alpha gradually decrease to baseline. Large quantities of proviral DNA are seen in the HIV-infected IFN alpha-treated cells with little evidence for viral transcription suggesting true microbiological latency. While most viral infections of cells result in IFN production, HIV is a notable exception. Indeed, HIV does not induce monocytes to produce IFN alpha and blocks its production following poly(I).poly(c) stimulation. This allows HIV yet another mechanism to evade an important host antiviral response. Paradoxically, the appearance of IFN activity in sera of HIV-infected patients is associated with disease progression, not resolution. Recent observations showing that the interaction between HIV-infected monocytes and PBMC results in the production of IFN alpha s with reduced anti-HIV activity may help explain this paradox. Thus, IFN alpha plays an important but complex role in HIV disease. The elucidation of cellular factors that regulate the antiretroviral effects of IFN alpha may lead to the development of novel therapeutic strategies for HIV infection.

Animals↗
PubMed1991

Identification of a prominent 85-kDa cAMP-dependent phosphoprotein associated with late G1 phase in mitogen-stimulated B lymphocytes.

In order to elucidate late regulatory events which may be involved in the onset of S phase in B lymphocytes, we studied the effect of anti-Ig on phosphorylation of soluble proteins at late G1 phase. Stimulation of murine splenic B lymphocytes with anti-Ig and other mitogens for 18 h was found to be associated with a major increase in phosphorylation of an 85 kDa/pI approximately 5.3 cytosolic protein, conversely, stimulation of the cells with non-mitogenic stimuli did not induce the phosphorylation of pp85. The increase in phosphorylation of pp85 could not be detected after 30 min, was barely detectable after 6 h, but was very prominent after 18 h of stimulation with anti-Ig. Thus, the increase in phosphorylation of pp85 is not an early signal but is rather correlated with the late G1 phase. pp85 could not be detected in the nuclei of either control or stimulated cells. Stimulation of B cells for 30 min with forskolin induced the phosphorylation of pp85, while phorbol ester did not have any effect. The phosphorylation of pp85 was induced by the catalytic subunit of cAMP protein kinase. Comparison of the phosphopeptide map of pp85 phosphorylated by anti-Ig in intact cells to the phosphopeptide map phosphorylated by forskolin or by the catalytic subunit of cAMP protein kinase, showed a striking similarity indicating that cAMP protein kinase may be involved in phosphorylation of pp85 in mitogen-stimulated cells. An increase in intracellular cAMP levels at late G1 phase was found in B cells stimulated by mitogens. These results implicate an important role for cAMP-dependent phosphorylation events, specifically the phosphorylation of pp85/pI 5.3, at late G1 phase during the cell cycle.

Animals↗
PubMed1990

cAMP-independent effects of cholera toxin on B cell activation. I. A possible role for cell surface ganglioside GM1 in B cell activation.

Cholera toxin has been used as a tool to study the effects of cAMP on the activation of B cells but may have effects independent of its ability to elevate cAMP. We found five lines of evidence which suggested that cholera toxin suppressed mitogen-stimulated B cell activation through a cAMP-independent pathway. 1) Cholera toxin (1 microgram/ml) was consistently more suppressive than forskolin (100 microM) despite the induction of higher intracellular cAMP levels by forskolin. 2) Cholera toxin was more suppressive at 1 microgram/ml than at 0.1 microgram/ml despite equivalent elevations of cAMP. 3) Washing B cells following their incubation with cholera toxin reversed much of the inhibition without altering intracellular cAMP levels. 4) The A subunit of cholera toxin, which at high concentrations (10 micrograms/ml) induced levels of cAMP comparable to those induced by cholera toxin (1 and 0.1 microgram/ml), did not inhibit B cell activation. 5) cAMP derivatives at high concentrations were much less effective than was cholera toxin in suppressing B cell activation. Although the elevation of cAMP may cause a mild inhibition of B cell proliferation, we found that even a marked elevation of cAMP did not suppress B cell proliferation, unless the elevation was persistent. We did, however, observe that the degree of toxin inhibition more closely paralleled binding of the toxin to B cells than toxin stimulation of cAMP. This result raised the possibility that binding of cholera toxin to its ganglioside GM1 receptor mediated an inhibitory signal which suppressed B cell proliferation.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1990

Effects of cholera toxin on human B cells. Cholera toxin induces B cell surface DR expression while it inhibits anti-mu antibody-induced cell proliferation.

Experiments were performed to investigate the effect of cholera toxin (CT) on human B cell function. Highly purified (greater than 98% CD20+) human peripheral blood B cells were exposed to CT in the presence or absence of anti-mu antibody. Treatment of highly purified B cells with CT stimulated enhanced expression of surface DR molecules, whereas it did not enhance expression of other B cell surface activation markers including transferrin or IL-2R. Neither the A nor the B subunits of CT by themselves enhanced the expression of surface DR Ag. In addition, 8-bromo-cAMP alone or in combination with the B subunit did not increase the expression of human B cell surface DR Ag. These findings suggest that neither elevation of cAMP nor binding to GM1 ganglioside are sufficient to stimulate this activation parameter in B cells. Associated with CT-mediated enhanced expression of MHC class II molecules we found that CT-treated B cells also served as stronger stimulators, compared with control cells, of both autologous and allogeneic MLR responses in peripheral blood T cells. Although CT stimulated early events in B cell activation, it inhibited anti-mu antibody-induced B cell thymidine incorporation by 55 to 75%. Inhibitory effects of CT were observed even when CT was added to cultures as late as 36 h after the addition of the anti-mu antibody. These results suggest that CT has both a stimulatory and inhibitory effect on human B cells and that the stimulatory effect may be mediated via a cAMP-independent mechanism.

8-Bromo Cyclic Adenosine Monophosphate↗