Regulation of platelet‐activating factor receptor expression in human B cells and B cell lines

Abstract

We extended our previous data regarding the modulation of human platelet-activating factor receptor (hPAF-R) expression on human B cell lines as well as normal B cells. First, we showed that hPAF-R mRNA was present in B cell lines expressing membrane hPAF-R, but was absent from cell lines devoid of hPAF-R. Second, enhanced hPAF-R membrane expression induced in IM9 line by IL4 was preceeded by hPAF-R mRNA accumulation that was detectable by 8 h and which peaked at 24 h. Similar results were observed for 10 nM platelet-activating factor treatment, which increased hPAF-R mRNA content up to 120% at 48 h, whereas hPAF-R membrane expression was up-regulated by 130%. Third, our data indicate that functional hPAF-R are expressed on resting, as well as on activated, B cells and that B cell activation is required for maintaining hPAF-R membrane and mRNA expression. Thus, in normal B cells, as well as in B cell lines, transcriptional regulation and/or messenger stability control hPAF-R expression.

Activation Via Multiple Signaling Pathways Induces Down-Regulation of Platelet-Activating Factor Receptors on Human B Lymphocytes

“…Phorbol ester is another extensively studied regulator of PAFR. Although most studies suggest that PKC activation negatively modulates PAFR expression or its response to PAF (23,24,48,49), other reports indicate opposite effects (11,28). Some cytokines, inflammatory mediators, and hormones have also been shown to modulate PAFR in various cell types (6).…”

“…Nguer et al (11) reported that PMA increased PAFR mRNA and surface expression in human tonsillar B cells. They also found that PDB/ION increased PAF binding to human peripheral blood B cells (10). There are several possibilities accounting for these discrepancies.…”

“…Our laboratory has identified that PAFR is present on B cell lines and human tonsillar B lymphocytes (7)(8)(9)(10)(11). We have reported that germinal center (GC) B cells express increased PAFR mRNA and have greater intracellular calcium ([Ca 2ϩ ] i ) responses compared with more mature mantle zone B cells (12).…”

“…It has been shown in B cells that PAFR binding and mRNA expression can be up-regulated by TGF-␤ (21,22), IL-4, or Cowan I strain Staphylococcus aureus (10,11). Phorbol esters have been reported to up-regulate (10,11) or diminish (23,24) PAFR on B lymphocytes and other cell types. In addition, there is no data on the expression of PAFR following engagement of the B cell Ag receptor (BCR).…”

No evidence for a putative involvement of platelet‐activating factor in systemic lupus erythematosus without active nephritis

“…PAF is known to enhance, in vitro, the number of its own receptors on blood cell types such as monocytes and lymphocytes. 27,28 Speculating that if PAF acts during SLE it might have a similar effect, we thus investigated the presence of membrane PAF-R on circulating blood cells of SLE patients. Our results indicate that PAF-R is not detected on lymphocytes, monocytes and granulocytes of SLE patients without active nephritis.…”