Signaling Cross-Talk between MHC Class II Molecular Conformers in Resting Murine B Cells

Abstract

In addition to functioning as a ligand to engage TCRs and drive TCR signaling, MHC class II molecules are signaling molecules that generate a number of signals within APCs, such as B lymphocytes. Moreover, MHC class II signaling is critical for B cell activation and development of a robust humoral immune response. Murine class II molecules exist in two distinct conformational states, based primarily on the differential pairing of transmembrane domain GxxxG dimerization motifs (i.e., M1-and M2-paired class II). This laboratory has previously reported that the binding of a multimerized form of an anti-class II mAb that selectively recognizes M1-paired I-A k class II drives intracellular calcium signaling in resting murine B cells and that this signaling is dependent on both src and Syk protein tyrosine kinase activity. In contrast, multimerized forms of two different anti-I-A k mAbs that bind both M1-and M2-paired class II fail to elicit a response. In this report, a flow cytometry-based calcium flux assay is used to demonstrate that coligation of M1-and M2-paired I-A k class II results in the active and selective inhibition of M1-paired I-A k class II B cell calcium signaling by M2-paired class II molecules. Because M1-and M2-paired class II can be loaded with different sets of peptides derived from Ags acquired by distinct pathways of endocytosis, these findings suggest an MHC class II signaling-based mechanism by which CD4 T cells of differing specificities can either enhance or suppress B cell activation. ImmunoHorizons, 2019, 3: 28-36.

Differential pairing of transmembrane domain GxxxG dimerization motifs defines two HLA-DR MHC class II conformers

“…, M1-and M2-pairing) and revealed the impact of TM domain pairing on the expression of the Ia.2 epitope recognized by the 11-5.2 mAb ( 10 , 11 ). Additional studies using the 11-5.2 mAb, which specifically binds M1-paired I-A k class II, demonstrate selective partitioning of M1-paired I-A k molecules into membrane microdomains colloquially termed “lipid rafts” ( 9 ) and reveal the unique signaling properties of these raft-resident class II molecules ( 13 , 14 ). 11-5.2 mAb blocking studies reveal the central role of M1 paired I-A k molecules in in vivo T cell activation ( 12 ) as well as in vitro B cell–T cell interactions ( 9 ).…”

“…While M1-paired mouse class II molecules represent a numerically minor fraction of all cell surface class II molecules, they drive important class II functions such as stimulation of naive T cells ( 12 ), formation of B cell-T cell conjugates ( 9 ), MHC class II signaling ( 13 , 14 ), and are selectively loaded with peptides derived from BCR-bound antigen ( 1 , 15 ). In contrast, the more abundant M2-paired class II molecules can actively block signaling by M1-paired class II ( 13 ), and are more readily loaded with peptides derived from non-cognate antigens ( 1 ). The roles of M1-and M2-paired class II molecules in the immune response have been recently reviewed ( 1 , 4 ).…”

Construction and evaluation of a self-replicative RNA vaccine against SARS-CoV-2 using yellow fever virus replicon

“…The difference between humoral immunity and cellular immunity stimulations could be attributed to the expression pattern of S protein. The intracellular antigen is presented by MHC class I and stimulates cellular immunity, whereas the extracellular antigen is presented by MHC class II and stimulates humoral immunity [ 41 , 42 ]. This study expressed S protein as a fused protein with prM (1 st –17 th amino acids) and E (transmembrane region) of YFV.…”

Reverse Signaling by MHC-I Molecules in Immune and Non-Immune Cell Types

“…While stimulated MHC-II molecules present in lipid rafts of antigen-presenting cells can signal via tyrosine kinases to ensure activation, maturation or proliferation, the MHC-II molecules that are relocated to non-raft regions can signal via protein kinase C to induce cell death (131). Likewise, in murine B cells the way in which the aand b-chains of MHC-II interact with each other creates different conformers, 10% of which locate preferentially in lipid rafts where they interact with the B cell receptor (BCR) partner CD79 to induce tyrosine kinase activity (139). Other intracellular reverse MHC-II signaling events similar to reverse MHC-I signaling are for example tyrosine phosphorylation and activation of Src, AKT, ERK and JNK (135).…”