REGULATION OF PLATELET-ACTIVATING-FACTOR RECEPTOR EXPRESSION IN HUMANB-CELLS AND B-CELL LINES

We extended our previous data regarding the modulation of human platel et-activating factor receptor (hPAF-R) expression on human B cell line s as well as normal B cells. First, we showed that hPAF-R mRNA was pre sent in B cell lines expressing membrane hPAF-R, but was absent from c ell lines devoid of hPAF-R. Second, enhanced hPAF-R membrane expressio n 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 in creased hPAF-R mRNA content up to 120% at 48 h, whereas hPAF-R membran e expression was up-regulated by 130%. Third, our data indicate that f unctional hPAF-R are expressed on resting, as well as on activated, B cells and that B cell activation is required for maintaining hPAF-R me mbrane and mRNA expression. Thus, in normal B cells, as well as in B c ell lines, transcriptional regulation and/or messager stability contro l hPAF-R expression.