Abstract Abstract 4855 It was demonstrated that TNF superfamily proteins may affect significantly the time of leukemic cells' survival in the course of B-cell chronic lymphocytic leukemia (B-CLL). The aim of our study was to evaluate the expression and release of BAFF (B-cell activating factor), APRIL (a proliferation-inducing ligand) and TRAIL (TNF-related apoptosis inducing ligand) molecules belonging to the cytokines of the superfamily of the tumor necrosis factor (TNF) by neutrophils (PMNs) and, for comparison, B cells isolated from the blood of patients with B-CLL vs. their concentration in the blood serum. 40 patients suffering from B-CLL and a control group of 15 healthy subjects were included in the study. Cytoplasmic fractions of PMNs and B cells were analyzed with the use of western blotting for the presence of TRAIL, BAFF and APRIL. Soluble TRAIL, BAFF and APRIL in the culture supernatants and the serum were assessed using ELISA kits. PMNs and B cells of patients with B-CLL before treatment demonstrated the statistically significantly higher expression of APRIL and BAFF proteins in comparison in relation to the control group of healthy subjects. In contrast, the expression of TRAIL protein in both types of cells of patients was statistically significantly lower than its expression in the control cells. In the supernatants of PMN and B lymphocytes of patients the decreased concentrations of sBAFF, unchanged of APRIL and increased of sTRAIL molecules were demonstrated. The results of studies carried out in patients with B-CLL before treatment indicate that the relations demonstrated between APRIL, BAFF and TRAIL molecules, released by neutrophils and B cells and relations between their concentrations in the serum can significantly influence the development of B-CLL. Disclosures: No relevant conflicts of interest to declare.