V M Sanders

Cellular Interactions in the Humoral Immune Response

Publisher Summary This chapter discusses the interactions between T and B cells and the role of accessory cells and cytokines in the generation of specific antibody responses. The first part of the chapter is a historic perspective followed by a summary of the present-day concepts. The final part of the chapter speculates on how the different components of the immune system might function in vivo. A highly complex system of communication has developed among the various cell types in the immune sytem. One important mechanism of communication is the requirement for interactions among cells for the activation and differentiation of resting B lymphocytes into antibody-secreting cells. These cellular interactions involve both cell-cell contact and the release of mediators (cytokines) that can act in either an autocrine or paracrine fashion on cells both within and outside the immune system. The chapter describes two types of functionally different Th cells and the role of lymphokines in the regulation of T and B cell function. Although Th1 versus Th2 cells have different effects on B cells and other cells in vitro, their role in vivo is less well understood. Nonetheless, studies in vivo have confirmed the requirement for IL-4 and IFN-У in IgE and IgG2, responses, respectively.

B cell-associated LFA-1 and T cell-associated ICAM-1 transiently cluster in the area of contact between interacting cells☆

TNP-specific B cells interact with carrier-specific T hybridoma cells in an antigen-specific, MHC-restricted manner. The formation of T cell/B cell conjugates is time and temperature dependent and results in the formation of a broad area of close contact between the interacting cells. In order to determine which surface molecules on the two cells cluster at the interaction site. T cell/B cell conjugates were formalin-fixed at different times following conjugation and were stained with antibodies directed against cell surface molecules. Results of these studies indicate that the alpha- and beta-subunits of LFA-1 on B cells transiently cluster in the area of cell contact. Maximum clustering of LFA-1 occurs at 45 min, after which time LFA-1 redistributes on the surface of the B cells. Several other B cell-associated molecules (MHC Class II, ICAM-1, Ig, B220, J11D, or CD23) do not cluster at the interaction site at any time point. T cell-associated LFA-1 does not cluster with any specific pattern, but ICAM-1 does. Maximum clustering of ICAM-1 occurs 60 to 90 min after intercellular contact. After this time, ICAM-1 redistributes on the surface of the T cells. Although both the alpha- and beta-subunits of LFA-1 cluster at the interaction site on B cells, antibodies recognizing these subunits differ in their ability to affect conjugation. One antibody recognizing the alpha chain of LFA-1 (M17/4.2) inhibits T-cell/B cell conjugation, whereas another antibody that also recognizes the alpha chain-(G-48) enhances conjugation. In contrast, an antibody that recognizes LFA-1 beta (M18/2.a.8) has no effect. An antibody that recognizes ICAM-1 (YN/1.7), the ligand for LFA-1, inhibits conjugation. These data show that, during T cell/B cell interaction. LFA-1 on B cells and ICAM-1 on T cells transiently cluster with similar, albeit not identical, kinetics to the site of cell-cell contact.

Purification and characterization of antigen-binding virgin and memory B cells

Publisher Summary This chapter focuses on the methods for purifying resting antigen-specific B cells so that their activation by antigens and T cells can be assessed. Many methods for studying the physiology and activation of B lymphocytes are available. The chapter describes a method for purifying a population of TNP-specific B cells (TNP-ABC) from spleens of normal or primed mice. These cells are suitable for the analysis of early activation events of B cells in response to antigen. However, to interpret such data, an accurate measurement of the purity of the enriched population is required. The antigen-binding capacity of these cells as measured by rosetting or binding fluorescent antigen gives a far higher estimate of purity than functional assays, such as proliferation, plaque formation, and an enumeration of clones in the splenic focus assay.