A Function for Ly-1+ B Cells

Abstract

During the last decade, there have been a number of documented sightings of Ly-1⁺ (CD5⁺/Leu-1⁺) B cells in both murine and human experimental systems. Despite these sightings and despite the circumstantial evidence linking Ly-1⁺ B cells to disease, the contribution of this B cell subset to normal or pathologic immune responses has not been defined. In this report, we will consider some of the unusual characteristics of Ly-1⁺ B cells and try to demonstrate that most of these traits can be accommodated by the working hypothesis that Ly-1⁺ B cells can serve as regulators of B cell development and/or function.

Before constructing this hypothesis, we will review some of the peculiarities of Ly-1⁺ B cells. Special emphasis will be placed on (i) Ly-1⁺ B cell tissue distribution and ontogeny, (ii) restrictions governing Ly-1⁺ B cell immunoglobulin heavy or light chain usage and repertoire development, (iii) the theory that Ly-1⁺ B cells represent a separate B cell lineage, and (iv) the association of Ly-1⁺ B cells to autoimmunity, lympho-proliferation, and transformation.

Ly-1⁺ Cell Distribution and Ontogeny Before 1980, the expression of cell surface antigens by lymphocyte subpopulations was determined primarily by cytotoxicity studies or by immunohistochemistry. By using these relatively nonquantitative methods, Led-better et al. (1) first suggested in 1980 that cells residing in B cell areas of lymph nodes expressed low levels of the Lyt-1 antigen. The subsequent identification of a number of murine B cell lymphomas which stained with monoclonal anti-Lyt-1 antibodies confirmed that B cells could express this formerly T cell-associated glycoprotein (2). With the advent of flow cytometry, it was possible to quantitate the expression of Lyt-1 on normal B lymphocytes. In 1982, Manohar et al. (3) documented the coexpression of IgM and Lyt-1 (then referred to as Ly-1) on splenocytes from normal mice (3) and demonstrated that Ly-1 expression on B cells was more subtle (up to 1 log duller staining) than on T cells.