High CD40 membrane expression in AIDS-related lymphoma B cell lines is associated with the CD45RA⁺, CD45RO⁺, CD59⁺ phenotype and high level of its soluble form in culture supernatants

CD40 is a membrane glycoprotein expressed on normal and neoplastic B lymphocytes. Stimulation through CD40 regulates important cellular functions, but the effects depend on its membrane density. While extensive studies have characterized CD40 in non-Hodgkin lymphomas of immunocompetent individuals, little is known on the characteristics of this molecule in lymphomas arising in immunocompromised hosts. The aim of this study was to characterize the pattern of CD40 expression in an in vitro model constituted by AIDS small non-cleaved lymphoma (SNCCL) cell lines. The analysis of CD45 isoforms, a group of molecules alternatively spliced during B cell differentiation, has been chosen to correlate this process to the number of CD40 molecules per cell in these cell lines. Since Apo 1/Fas expression is upregulated on B lymphocytes after CD40 ligation and this expression is functionally relevant, we wanted to know whether a different CD40 pattern in AIDS-SNCCL cell lines could influence CD95 expression. We have shown that 3 of these cell lines (PA 682, Es III, and HBL-2) have high membrane CD40 expression (>100,000 molecules/cell); they release large amounts of soluble CD40 (sCD40) in culture supernatants (>500 pg/ml), are CD45RA/RO double labelled, and express the Apo 1/Fas (CD95) antigen. On the contrary, low CD40 membrane antigen cell lines (BRGIgA, HBL-2, NC 71, AS 283A, and LAM C3+, <50,000 molecules/cell) release low amounts of sCD40 (<300 pg/ml), are CD45RA⁺ but CD45RO^-, and do not express CD95. EBV has no role in CD40 and CD45 isoform behaviour, because EBV superinfection of the EBV negative, low membrane CD40 HBL-2 cell line does not modify CD40 membrane expression, sCD40 production, or CD45 isoform and CD95 expression. Our data suggest that membrane CD40 in AIDS-SNCCL cell lines might be a key element in the regulation of their pathophysiology by influencing the expression of CD45 isoforms and of CD95, and by the release of its soluble form.