Induction of CD5 on B and T cells is suppressed by cyclosporin A, FK-520 and rapamycin

Abstract

The expression of CD5 can be induced on murine B-2 cells by anti-IgM, a recognized analog of thymus-independent 2 type (TI-2) antigen. Given that cyclosporin A (CsA) sensitivity is a distinguishing feature of TI-2 type B cell activation, we asked whether the in vitro induction of CD5 on B cells by anti-mu is CsA sensitive. We report that anti-mu induced CD5 expression on B-2 cells was inhibited by CsA as well as FK-520 and rapamycin. When L-685,818, a FK-520 and rapamycin antagonist, was added to anti-mu stimulated B cell cultures containing FK-520 or rapamycin, but not CsA, suppression was abrogated and complete induction of CD5 was seen. When we used either CD4+CD8+ thymocytes or peripheral T cells activated by phorbol ester and ionomycin, the cell surface induction of CD5 was also partially blocked by CsA, FK-520 and rapamycin. Moreover, in both B and T cells, the same immunosuppressive drugs did not affect constitutive CD5 expression but only blocked de novo induction. To determine the level of CD5 regulation, we activated T cells using phorbol myristate acetate (PMA)/ionomycin and report that CD5 induction was sensitive to actinomycin D (AcD). Similarly, the induction of CD5 on anti-mu activated B cells was blocked by AcD. In addition, T cells that were activated by PMA/ionomycin expressed more abundant CD5 mRNA than CsA or FK-520 treated cells. Based on the CsA-sensitive regulation of CD5 we thought that the CsA-sensitive nuclear factor of activated T cells (NFAT) might be involved in CD5 regulation. We report evidence by Western blot analysis that NFATp is expressed by both resting and TI activated B cells but apparently not CD4+CD8+CD5+ thymocytes. We conclude that in both B and T cells the induction of CD5 requires transcriptional regulation, and that the inhibition of CD5 expression by the immunosuppressive drugs CsA, FK-520 and rapamycin requires drug-immunophilin complex formation.

B-cell activation by crosslinking of surface IgM or ligation of CD40 involves alternative signal pathways and results in different B-cell phenotypes.

“…The origin of CD5+ B cells is a matter of controversy; some investigators believe that they derive from a precommitted pool of fetal/ neonatal precursors (32). Others, including ourselves, believe that any naive [newly differentiated, "B-0" (36)] B cell can become CD5+ as a consequence of sIgM ligation (37,38).…”

3BP2 Deficiency Impairs the Response of B Cells, but Not T Cells, to Antigen Receptor Ligation

“…3BP2 Ϫ/Ϫ B cells responded normally to ionomycin with complete dephosphorylation of NF-ATp. BCR stimulation of splenic B cells induces NF-AT-dependent upregulation of surface CD5 expression (4,53). B cells from 3BP2 Ϫ/Ϫ mice were impaired in their ability to upregulate CD5 in response to BCR ligation (Fig.…”

Normal B-1a cell development requires B cell-intrinsic NFATc1 activity

“…To isolate splenic B-2 cells, spleens were disaggregated and red blood cells were lysed by treatment with ammonium chloride as described (13). Cells were stained for fluorescence-activated cell sorting (FACS) with biotinylated anti-CD3, biotinylated anti-Ter119, phycoerythrin (PE)-conjugated anti-CD5, FITC-conjugated anti-CD4, and PEconjugated anti-CD8 antibodies followed by secondary staining with PE-conjugated streptavidin.…”

“…We and others (11,12) previously showed that crosslinking of the B cell receptor (BCR) on splenic B cells, to partially mimic positive selection by self-antigen, induces several aspects of the B-1a phenotype, including the expression of CD5. We subsequently demonstrated that this induction of CD5 is cyclosporin-sensitive and requires an enhancer located Ϸ2 kb upstream of the CD5 coding sequences (13,14). This enhancer contains two functional nuclear factor of activated T cells (NFAT) sites (14) and is highly conserved in humans (15).…”