ABSTRACT
The major function of B lymphocytes is to sense antigens and to produce protective antibodies after activation. This function requires the expression of a B-cell antigen receptor (BCR), and evolutionary conserved mechanisms seem to exist that ensure that B cells without a BCR do not develop nor survive in the periphery. Here, we show that the loss of BCR expression on Burkitt lymphoma cells leads to decreased mitochondrial function and impaired metabolic flexibility. Strikingly, this phenotype does not result from the absence of a classical Syk-dependent BCR signal but rather from compromised ER expansion. We show that the reexpression of immunoglobulins (Ig) in the absence of the BCR signaling subunits Igα and Igß rescues the observed metabolic defects. We demonstrate that immunoglobulin expression is needed to maintain ER homeostasis not only in lymphoma cells but also in resting B cells. Our study provides evidence that the expression of BCR components, which is sensed in the ER and shapes mitochondrial function, represents a novel mechanism of metabolic control in B cells.
Subject(s)
B-Lymphocytes/metabolism , Burkitt Lymphoma/metabolism , Endoplasmic Reticulum/immunology , Immunoglobulin M/metabolism , Signal Transduction/genetics , Animals , Burkitt Lymphoma/pathology , Cell Line, Tumor , Gene Knockout Techniques , Homeostasis/genetics , Homeostasis/immunology , Humans , Immunoglobulin M/genetics , Mice , Mice, Transgenic , Mitochondria/metabolism , Phenotype , Receptors, Antigen, B-Cell/genetics , Receptors, Antigen, B-Cell/metabolism , Signal Transduction/immunology , Syk Kinase/deficiency , Syk Kinase/genetics , Transduction, GeneticABSTRACT
B cells contribute critically to an effective immune response by producing Ag-specific Abs. During the immune response to so-called "thymus-dependent Ags," activated B cells seek T cell help and form germinal centers. In contrast, thymus-independent Ags generally do not induce germinal center formation. In the germinal center, B cells undergo somatic hypermutation, affinity-based clonal expansion, and differentiation to produce plasma cells and memory B cells. Valuable insight into these processes has been gained by using model hapten-carrier complexes or SRBCs. SRBCs induce robust germinal center formation in mice. Therefore, this Ag is commonly used to study germinal center responses. In contrast to haptenated Ags, thus far it has been difficult to measure the titer of Ag-specific Abs or the expansion of Ag-specific B cells after immunization with SRBCs. We have developed new, simple methods to access these parameters, thus providing new tools to study germinal center and Ab responses.
