Reversible anergy of sIgM-mediated signaling in the two subsets of CLL defined by VH-gene mutational status

Abstract

The 2 subsets of chronic lymphocytic leukemia (CLL), of worse or better prognosis, likely derive from pre-GC unmutated B cells, or post-GC mutated B cells, respectively. Different clinical behavior could relate to the ability of tumor cells to respond to surface (sIg)–mediated signals. Unmutated cases (U-CLL) have an increased ability to phosphorylate p72^Syk in response to sIgM ligation compared to mutated cases (M-CLL). We now confirm and further investigate this differential signaling in a large cohort by [Ca²⁺]_i mobilization. Cases responding to sIgM ligation express higher levels of CD38, ZAP-70, and sIgM. However, CD38 does not influence signaling in vitro or associate with response in bimodal CD38-expressing cases. Similarly, ZAP-70 expression is not required for response in either U-CLL or M-CLL. Strikingly, partially or completely anergized sIgM responses from each subset can recover both sIgM expression and signal capacity spontaneously in vitro or following capping/endocytosis. This provides direct evidence for engagement of putative antigen in vivo. Signaling via sIgD differs markedly being almost universally positive in both U-CLL and M-CLL, with no association with CD38 or ZAP-70 expression. Downstream signaling pathways, therefore, appear intact in CLL, locating anergy to sIgM, mainly in M-CLL. Integration of differential isotype-specific effects mediated by (auto)antigen may determine tumor behavior.