RESUMO
Small, soluble metabolites not only are essential intermediates in intracellular biochemical processes, but can also influence neighbouring cells when released into the extracellular milieu1-3. Here we identify the metabolite and neurotransmitter GABA as a candidate signalling molecule synthesized and secreted by activated B cells and plasma cells. We show that B cell-derived GABA promotes monocyte differentiation into anti-inflammatory macrophages that secrete interleukin-10 and inhibit CD8+ T cell killer function. In mice, B cell deficiency or B cell-specific inactivation of the GABA-generating enzyme GAD67 enhances anti-tumour responses. Our study reveals that, in addition to cytokines and membrane proteins, small metabolites derived from B-lineage cells have immunoregulatory functions, which may be pharmaceutical targets allowing fine-tuning of immune responses.
Assuntos
Linfócitos B/metabolismo , Interleucina-10/imunologia , Macrófagos/metabolismo , Neoplasias/imunologia , Ácido gama-Aminobutírico/metabolismo , Animais , Linfócitos B/imunologia , Linfócitos T CD8-Positivos/imunologia , Linfócitos T CD8-Positivos/metabolismo , Proliferação de Células , Feminino , Deleção de Genes , Glutamato Descarboxilase/deficiência , Glutamato Descarboxilase/genética , Humanos , Inflamação/imunologia , Inflamação/prevenção & controle , Macrófagos/imunologia , Masculino , Camundongos , Neoplasias/patologia , Linfócitos T Citotóxicos/imunologia , Linfócitos T Citotóxicos/metabolismo , Ácido gama-Aminobutírico/biossínteseRESUMO
Positive selection of high-affinity B cells within germinal centers (GCs) drives affinity maturation of antibody responses. Here, we examined the mechanism underlying the parallel transition from immunoglobulin M (IgM) to IgG. Early GCs contained mostly unswitched IgM+ B cells; IgG+ B cells subsequently increased in frequency, dominating GC responses 14-21 days after antigen challenge. Somatic hypermutation and generation of high-affinity clones occurred with equal efficiency among IgM+ and IgG+ GC B cells, and inactivation of Ig class-switch recombination did not prevent depletion of IgM+ GC B cells. Instead, high-affinity IgG+ GC B cells outcompeted high-affinity IgM+ GC B cells via a selective advantage associated with IgG antigen receptor structure but independent of the extended cytoplasmic tail. Thus, two parallel forms of GC B-cell-positive selection, based on antigen receptor variable and constant regions, respectively, operate in tandem to ensure high-affinity IgG antibodies predominate in mature serum antibody responses.
