Leptin, one of the adipokines, functions as a hormone and a cytokine. In this investigation, we show for the first time that leptin, in a concentration-dependent manner, activates human peripheral blood B cells to induce secretion of IL-6, IL-10, and TNF-α. Leptin increased B cells expressing CD25 and HLA-DR. Leptin induces phosphorylation of Janus activation kinase 2 (JAK2), signal transducer and activator of transcription 3 (STAT3), p38 mitogen-activated protein kinase (p38MAPK), and extracellular signal-regulated kinase (ERK1/2). Furthermore, leptin-induced cytokine secretion by B cells was blocked by inhibitors of JAK2, STAT3, p38MAPK, and ERK1/2. These data demonstrate that leptin activates human B cells to secrete cytokines via activation of JAK2/STAT3 and p38MAPK/ERK1/2 signaling pathways, which may contribute to its inflammatory and immunoregulatory properties.

Aging is associated with increased susceptibility to microbial infections, and monocytes play an important role in microbial defense. In this study, we have identified and compared four subpopulations of monocytes (CD14++(high)CD16−, CD14+(low)CD16−, CD14++(high)CD16+, and CD14+(low)CD16+) in the peripheral blood of young and aged subjects with regard to their numbers, cytokine production, TLR expression, and phosphorylation of ERK1/2 in response to pam3Cys a TLR-1/2 ligand. Proportions and numbers of CD14++(high)CD16+ and CD14+(low)CD16+ monocytes were significantly increased, whereas proportions of CD14+(low)CD16− monocytes were decreased in aged subjects as compared to young subjects. In aged subjects, IL-6 production by all four subsets of monocytes was significantly decreased, whereas TNF-α production was decreased in monocyte subsets, except the CD14+(low)CD16− subset. A significantly reduced expression of TLR1 was observed in CD14++(high)CD16+ and CD14+(low)CD16+ monocyte subsets in aged subjects. Furthermore, following pam3Cys stimulation, ERK1/2 phosphorylation was significantly lower in CD14+(low)CD16+, CD14++(high)CD16+, and CD14+(low)CD16− subsets of monocytes from aged subjects. This is the first study of four subpopulations of monocytes in aging, which demonstrates that their functions are differentially impaired with regard to the production of cytokines, expression of TLR, and signaling via the ERK–MAPK pathway. Finally, changes in the number of monocyte subsets, and impairment of TLR1 expression, TNF-α production, and EK1/2 phosphorylation was more consistent in CD16+ monocyte subsets regardless of expression of CD14high or CD14+low, therefore highlighting the significance of further subdivision of monocytes into four subpopulations.

End-stage renal disease (ESRD) is associated with increased propensity to infections, diminished response to vaccination, impaired cell-mediated immunity, and reduced CD4+/CD8+ T-lymphocyte ratio. Four subsets of CD4+ and CD8+ T cells have been recently identified: naïve cells (as yet uncommitted), central memory (CM) cells (previously programmed), and CD45RA-positive and CD45RA-negative effector memory (EM) cells (programmed to perform specific effector functions). The effect of ESRD on subpopulations of T lymphocytes is unclear and was studied here. Twenty-one hemodialysis patients and 21 age-matched controls were studied. Pre- and post-dialysis blood samples were obtained and analyzed by three-color flow cytometry. CD4+/CD8+ ratio and the numbers of the naïve and CM CD4+ and CD8+ T cells were significantly reduced, whereas the numbers of EM CD4+ and CD8+ T cells were unchanged in the ESRD group. The reduction of the naïve and CM T-cell counts in the ESRD group was associated with increased apoptosis of these cells. Negative correlations were found between severity of azotemia, oxidative stress, and hyperphosphatemia with the number of naïve T cells. Comparison of diabetic with non-diabetic ESRD patients revealed higher numbers of total CD8+ cells and EM CD8+ T cells in the diabetic group. Dialysis did not significantly change the naïve and CM CD4+ or CD8+ cell counts, but significantly lowered CD8+ EM cell count. Thus, ESRD results in increased apoptosis and diminished populations of naïve and CM T lymphocytes. This phenomenon may, in part, contribute to the impaired immune response in this population.

Background. End-stage renal disease (ESRD) results in increased susceptibility to infections, impaired response to vaccination and diffuse B-cell lymphopenia. However, the precise nature and mechanism of ESRD-induced B-cell lymphopenia remains unclear. Therefore, we studied the distribution of major B-cell subsets, B-cell growth, differentiation and survival factors, IL-7 and BAFF, and their receptors in 21 haemodialysis patients and 21 controls.Methods. Innate B1 cells (CD19+, CD5+), conventional B2 cells (CD19+, CD5−), newly formed transitional B cells (CD19+, CD10+, CD27−), naïve B cells (CD19+, CD27−) and memory B cells (CD19+, CD27+) and BAFF receptor were quantified by flow cytometry. Plasma IL-7, BAFF, IL-6, TNF-α and IL-10 were measured by ELISA.Results. The ESRD group exhibited significant reductions of all B-cell subpopulations except for transitional B cells that were less severely affected. No significant difference was found in B-cell apoptosis between the ESRD and control groups. Moreover, plasma IL-7 and BAFF levels were elevated in ESRD patients, therefore excluding their deficiencies as a possible culprit. However, BAFF receptor expression was significantly reduced in transitional but not mature B cells in the ESRD group. Interestingly, B-cell activation with the TLR9 agonist resulted in significantly greater production of IL-6 and TNF alpha but not IL-10 in the ESRD group.Conclusions. Thus, despite elevation of B-cell growth, differentiation and survival factors, ESRD patients exhibited diffuse reduction of B-cell subpopulations. This was associated with the down-regulation of BAFF receptor in transitional B cells. The latter can, in part, contribute to B-cell lymphopenia by promoting resistance to the biological actions of BAFF that is a potent B-cell differentiation and survival factor.

Background: End-stage renal disease (ESRD) is simultaneously associated with inflammation, impaired immunity and increased susceptibility to microbial infections. Innate immune cells, monocytes and polymorphonuclear leukocytes (PMN) recognize pathogens via toll-like receptors (TLR) triggering phagocytosis, cellular activation and secretion of inflammatory cytokines. Data on expression and function of TLRs in ESRD are limited. Methods: Blood samples from 21 stable ESRD patients and 21 normal controls were processed for TLR2, TLR4, TLR7 and TLR 9 expression on monocytes and PMN by flow cytometry. TLR activity was examined by determining the response to TLR4 and TLR2 ligands. Results: The ESRD group exhibited significant upregulation of TLR2 and TLR4 (but not TLR7 or TLR 9) expressions on monocytes and of TLR4 on PMN. This was coupled with heightened cytokine production in response to TLR4 activation with lipopolysaccharide. However, the response to TLR2 stimulation with peptidoglycan was unchanged in the ESRD group. Conclusions: Monocyte TLR2 and TLR4 and neutrophil TLR4 expressions and TLR4 activity are increased hemodialysis patients, representing another dimension of ESRD-associated inflammation.