RESUMEN
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 [Ca(2+)](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.
Asunto(s)
Antígenos de Superficie/fisiología , Anergia Clonal/genética , Inmunidad Celular/genética , Inmunoglobulina M/fisiología , Región Variable de Inmunoglobulina/genética , Leucemia Linfocítica Crónica de Células B/genética , Leucemia Linfocítica Crónica de Células B/inmunología , ADP-Ribosil Ciclasa 1/genética , Señalización del Calcio/inmunología , Endocitosis/inmunología , Regulación Leucémica de la Expresión Génica , Humanos , Inmunoglobulina D/metabolismo , Inmunoglobulina M/genética , Inmunoglobulina M/metabolismo , Leucemia Linfocítica Crónica de Células B/clasificación , Leucemia Linfocítica Crónica de Células B/diagnóstico , Glicoproteínas de Membrana/genética , Mutación , Pronóstico , Receptor Cross-Talk/inmunología , Transducción de SeñalRESUMEN
PURPOSE: To determine the origin and relationship of the rare IgG+ variant of chronic lymphocytic leukemia (CLL) to the two common IgM+IgD+ subsets that are distinguished by expression of unmutated or mutated V(H) genes, with the former having a worse prognosis. EXPERIMENTAL DESIGN: IgG+ CLL cells were characterized using phenotypic, functional, and immunogenetic analyses. RESULTS: IgG+ CLL was phenotypically similar to mutated IgM+IgD+ CLL (M-CLL) and variably expressed CD38 (4 of 14). ZAP-70, a tyrosine kinase preferentially expressed in unmutated CLL, was found in only 2 of 14 cases. The ability to signal via surface IgM (sIgM) varies between the main subsets of CLL and is associated with expression of ZAP-70. In IgG(+) CLL, 9 of 14 responded to engagement of sIgG with no apparent requirement for expression of CD38 or ZAP-70. However, signal capacity correlated with intensity of sIgG expression. Most switched immunoglobulin variable region genes were somatically mutated without intraclonal variation, and no case expressed activation-induced cytidine deaminase. Derivation from a postgerminal center B cell is, therefore, likely, and a relationship with M-CLL is suggested. This is supported by a shared biased usage of the V4-34 gene. Similar bias in normal B cells developed with age, providing an expanded population for transforming events. However, conserved sequences detected in the CDR3 of V4-34-encoded gamma chains were not found M-CLL, indicating no direct path of isotype switch from M-CLL. CONCLUSION: IgG+ CLL is likely to arise from an age-related expanded pool of B cells, on a path parallel to M-CLL, and perhaps with a similar clinical course.
