Distinct IRAK4 Expression in Normal and B-CLL Lymphocytes

Abstract

Toll-like receptors (TLR) signaling plays an important role in the B cell biology. It induces the maturation, proliferation and antibody production in response to pathogen recognition. Interleukin-1 Receptor-associated Kinase-4 (IRAK-4) is TLR downstream molecule which is of strategic importance in starting a cascade of NF-kappaB (Nuclear factor-kappaB) and MAPK (Mitogen-activated protein kinase) intracellular signaling pathways. The aim of the study was to identify the differences in IRAK-4 expression in normal and chronic lymphocytic leukemia (CLL) lymphocytes. We have also studied the IRAK-4 expression alteration upon TLR2/4 ligand stimulation in leukemic and normal B cells. We carried out Real-Time PCR and Western blot analysis of IRAK4 mRNA (RQ) and protein expression. The study were performed on the isolated CD19+ normal B lymphocytes and CLL cells (CD5+CD19+) before and 30 min after (Lipopolysaccharide) LPS and (Staphylococcus aureus strain Cowan I) SAC stimulation. IRAK-4 mRNA expression was significantly higher in normal CD19+ lymphocytes as compared to leukemic CD5+CD19+ subpopulation (RQ median 0.90 vs 0.54; p=0.012). In normal lymphocytes, LPS and SAC treatment led to significant IRAK-4 down-regulation both at mRNA (RQ median 0.90 vs 0.53 vs 0.40; p=0.03, p=0.01) and protein level, whereas generally there were no significant changes in IRAK-4 expression neither on mRNA nor protein level. No trend or significant differences in IRAK-4 expression in leukemic lymphocytes after LPS and SAC stimulation may imply the presence of alleged defect of immune tolerance in CLL.