Mechanical control of antigen detection and discrimination by T and B cell receptors

The adaptive immune response is orchestrated by just two cell types, T cells and B cells. Both cells possess the remarkable ability to recognize virtually any antigen through their respective antigen receptors-the T cell receptor (TCR) and B cell receptor (BCR). Despite extensive investigations into the biochemical signaling events triggered by antigen recognition in these cells, our ability to predict or control the outcome of T and B cell activation remains elusive. This challenge is compounded by the sensitivity of T and B cells to the biophysical properties of antigens and the cells presenting them-a phenomenon we are just beginning to understand. Recent insights underscore the central role of mechanical forces in this process, governing the conformation, signaling activity, and spatial organization of TCRs and BCRs within the cell membrane, ultimately eliciting distinct cellular responses. Traditionally, T cells and B cells have been studied independently, with researchers working in parallel to decipher the mechanisms of activation. While these investigations have unveiled many overlaps in how these cell types sense and respond to antigens, notable differences exist. To fully grasp their biology and harness it for therapeutic purposes, these distinctions must be considered. This review compares and contrasts the TCR and BCR, placing emphasis on the role of mechanical force in regulating the activity of both receptors to shape cellular and humoral adaptive immune responses.

The Mechanism of bnAb Production and Its Application in Mutable Virus Broad-Spectrum Vaccines: Inspiration from HIV-1 Broad Neutralization Research

Elite controllers among HIV-1-infected individuals have demonstrated a stronger ability to control the viral load in their bodies. Scientists have isolated antibodies with strong neutralizing ability from these individuals, which can neutralize HIV-1 variations; these are known as broadly neutralizing antibodies. The nucleic acid of some viruses will constantly mutate during replication (such as SARS-CoV-2), which will reduce the protective ability of the corresponding vaccines. The immune escape caused by this mutation is the most severe challenge faced by humans in the battle against the virus. Therefore, developing broad-spectrum vaccines that can induce broadly neutralizing antibodies against various viruses and their mutated strains is the best way to combat virus mutations. Exploring the mechanism by which the human immune system produces broadly neutralizing antibodies and its induction strategies is crucial in the design process of broad-spectrum vaccines.

Contrasting the In Situ Behavior of a Memory B Cell Clone During Primary and Secondary Immune Responses

Whether memory B cells possess altered differentiative potentials and respond in a qualitatively distinct fashion to extrinsic signals as compared with their naive precursors is a current subject of debate. We have investigated this issue by examining the participation of a predominant anti-arsonate clonotype in the primary and secondary responses in the spleens of A/J mice. While this clonotype gives rise to few Ab-forming cells (AFC) in the primary response, shortly after secondary immunization its memory cell progeny produce a massive splenic IgG AFC response, largely in the red pulp. Extensive clonal expansion and migration take place during the secondary AFC response but Ab V region somatic hypermutation is not reinduced. The primary and secondary germinal center (GC) responses of this clonotype are both characterized by ongoing V gene hypermutation and phenotypic selection, little or no inter-GC migration, and derivation of multiple, spatially distinct GCs from a single progenitor. However, the kinetics of these responses differ, with V genes containing a high frequency of total as well as affinity-enhancing mutations appearing rapidly in secondary GCs, suggesting either recruitment of memory cells into this response, or accelerated rates of hypermutation and selection. In contrast, the frequency of mutation observed per V gene does not increase monotonically during the primary GC response of this clonotype, suggesting ongoing emigration of B cells that have sustained affinity- and specificity-enhancing mutations.

Migration of Antigen-Presenting B Cells from Peripheral to Mucosal Lymphoid Tissues May Induce Intestinal Antigen-Specific IgA Following Parenteral Immunization

Parenterally administered immunizations have long been used to induce protection from mucosal pathogens such as Bordetella pertussis and influenza virus. We previously found that i.m. inoculation of mice with the intestinal pathogen, rotavirus, induced virus-specific Ab production by intestinal lymphocytes. We have now used adoptive transfer studies to identify the cell types responsible for the generation of virus-specific Ab production by gut-associated lymphoid tissue (GALT) after i.m. immunization. Three days after i.m. immunization with rotavirus, cells obtained from the draining peripheral lymph nodes of donor mice were transferred into naive recipient mice. We found that intestinal lymphocytes produced rotavirus-specific Igs (IgM, IgA, and IgG) 2 wk after transfer of either unfractionated cells, or unfractionated cells rendered incapable of cellular division by mitomycin C treatment. Additional studies demonstrated that rotavirus-specific IgA, but not IgG, was produced by intestinal lymphocytes after transfer of purified B cells. Ig allotype analysis revealed that rotavirus-specific IgA was produced by intestinal B cells of recipient origin, suggesting that migration of Ag-presenting B cells from peripheral lymphoid tissues to GALT may contribute to the generation of mucosal IgA responses after parenteral immunization. Strategies that promote Ag uptake and presentation by B cells may enhance mucosal IgA production following parenteral immunization.

A Mathematical Model on Germinal Center Kinetics and Termination

We devise a mathematical model to study germinal center (GC) kinetics. Earlier models for GC kinetics are extended by explicitly modeling 1) the cell division history of centroblasts, 2) the Ag uptake by centrocytes, and 3) T cell dynamics. Allowing for T cell kinetics and T-B cell interactions, we study the role of GC T cells in GC kinetics, GC termination, and B cell selection. We find that GC T cells play a major role in GC formation, but that the maintenance of established GC reactions requires very few T cells only. The results therefore suggest that the termination of a GC reaction is largely caused by lack of Ag on the follicular dendritic cells and is hardly influenced by Th cells. Ag consumption by centrocytes is the major factor determining the decay rate of the antigenic stimulus during a GC reaction. Investigating the effect of the Ag dose on GC kinetics, we find that both the total size of the GC and its duration are hardly influenced by the initial amount of Ag. In the model this is due to a buffering effect by competition for limited T cell help and/or competition between proliferating centroblasts.