Multiple sclerosis-associated CLEC16A controls HLA class II expression via late endosome biogenesis

C-type lectins are key players in immune regulation by driving distinct functions of antigen-presenting cells. The C-type lectin CLEC16A gene is located at 16p13, a susceptibility locus for several autoimmune diseases, including multiple sclerosis. However, the function of this gene and its potential contribution to these diseases in humans are poorly understood. In this study, we found a strong upregulation of CLEC16A expression in the white matter of multiple sclerosis patients (n = 14) compared to non-demented controls (n = 11), mainly in perivascular leukocyte infiltrates. Moreover, CLEC16A levels were significantly enhanced in peripheral blood mononuclear cells of multiple sclerosis patients (n = 69) versus healthy controls (n = 46). In peripheral blood mononuclear cells, CLEC16A was most abundant in monocyte-derived dendritic cells, in which it strongly co-localized with human leukocyte antigen class II. Treatment of these professional antigen-presenting cells with vitamin D, a key protective environmental factor in multiple sclerosis, downmodulated CLEC16A in parallel with human leukocyte antigen class II. Knockdown of CLEC16A in distinct types of model and primary antigen-presenting cells resulted in severely impaired cytoplasmic distribution and formation of human leucocyte antigen class II-positive late endosomes, as determined by immunofluorescence and electron microscopy. Mechanistically, CLEC16A participated in the molecular machinery of human leukocyte antigen class II-positive late endosome formation and trafficking to perinuclear regions, involving the dynein motor complex. By performing co-immunoprecipitations, we found that CLEC16A directly binds to two critical members of this complex, RILP and the HOPS complex. CLEC16A silencing in antigen-presenting cells disturbed RILP-mediated recruitment of human leukocyte antigen class II-positive late endosomes to perinuclear regions. Together, we identify CLEC16A as a pivotal gene in multiple sclerosis that serves as a direct regulator of the human leukocyte antigen class II pathway in antigen-presenting cells. These findings are a first step in coupling multiple sclerosis-associated genes to the regulation of the strongest genetic factor in multiple sclerosis, human leukocyte antigen class II

CD27(+) B cells in human lymphatic organs: re-evaluating the splenic marginal zone

The marginal zone of human spleens is regarded as an organ-specific region harbouring sessile memory B cells. This opinion has arisen by extrapolating from results obtained in mice and rats. Detection of CD27(+) B cells in situ now revealed similarities among the most superficial region of B-cell follicles in human spleens, reactive lymph nodes, inflamed appendices, tonsils and terminal ilea. The follicular surface in these organs consists of small naïve immunoglobulin D (IgD)(+) CD27(–) B cells predominating in an inner area and larger IgD(+/–) CD27(+) B cells prevailing in a more superficial position. CD27(+) B cells may, however, also occupy the entire follicular periphery around the germinal centre. Together with additional peculiarities this distribution indicates a fundamental microanatomical difference among the human and rodent splenic white pulp. We hypothesize that the follicular periphery represents a recirculation compartment both for naïve and memory/natural reactive B cells in all human secondary lymphatic organs. This assumption implies a difference in recirculation behaviour among human and rodent B memory cells

Quantitative and functional characteristics of intestinal-homing memory T cells: analysis of Crohn's disease patients and healthy controls

Circulating memory T cells can be subdivided on the basis of β7 integrin expression. The β7(+) population contains cells primed in the intestine capable of homing back to the gut. We hypothesized that cytokine production by β7(+) memory T cells reflects the specialized mucosal compartment in which they were primed. Flow cytometry of whole blood was used to assess numbers of β7(+) (β7(hi) and β7(int)) and β7(–) memory T cells and their production of Th1 and regulatory cytokines in healthy controls and Crohn's disease patients. In controls, β7(+) and β7(–) memory T cells displayed a similar qualitative profile of cytokine production but the β7(+) population was enriched for cytokine-producing effector cells. In addition, the β7(hi) population contained more cytokine-producing cells than the β7(int) population, suggesting a gradient of cytokine production based on β7 integrin expression. In active Crohn's disease, there was altered expression of β7 integrin with a decrease in intestinal-homing memory T cells and an increase in systemic memory T cells. Furthermore, there was a selective loss of IL-10 and increase in TGF-β in both β7(+) and β7(–) memory T cell subsets which may contribute to the pathogenesis of the inflammatory process in Crohn's disease