The CD5+ B cell: a B cell lineage with a central role in autoimmune disease?

Antigen-specific down-regulation of immunopathological events in an experimental autoimmune kidney disease

Heymann nephritis (HN) is an experimental autoimmune disease of rats characterized by immune-complex (IC) depositions on the epithelial side of the glomerular basement membrane (GBM) and by proteinuria. Several forms of HN have been produced by various investigators, but one thing has been common to all of them, namely their inducement by the development of pathogenic IgG autoantibodies (aabs). The aim of this review is to describe how pathogenic IgG aab production (which initiates and maintains the disease) in slowly progressive HN (SPHN) can be specifically terminated by injections of ICs made up of native rat renal tubular antigens and IgM antibodies directed against them.

Levels of CD5+ B cells are not increased in probands or relatives in a family study of primary Sjögren's syndrome

Levels of CD5+ B lymphocytes were assayed in a large family study of Primary Sjögren's syndrome. There was no significant difference in CD5 expression by index cases or their relatives when compared to controls. No association between CD5 expression, serological abnormalities or HLA haplotype was found and, furthermore, no evidence of linkage with HLA was observed. There was, however, variation in the expression of CD5+ B cells between the families. Levels in spouses were lower and reached statistical significance. The role for genetic and environmental factors influencing CD5 expression is discussed. Any genetic influence does not appear to involve the HLA region or genes in linkage disequilibrium.

The effect of improvements in cytometer sensitivity on the detection of CD5-positive B cells with dim fluorescence

When antigen density on the surface of a cell population is low and variable, the percentage of that population determined to express the antigen (i.e., to be positively stained) depends directly on the sensitivity of the flow cytometer for resolving particles which are dimly fluorescent from those which are unstained. In this study, the sensitivity of a commercial flow cytometer has been improved by changes in the photomultiplier tube, the fluorescence filter, and the amount of stray light entering the fluorescence channel. In a model system with human lymphocytes, modifications to these factors increased the percent of the B-lymphocyte population found to express the CD5 antigen.

An evolutionarily-conserved role for murine Ly-1 B cells in protection against bacterial infections

The murine Ly-1 B cell lineage, although comprising only a minority of peripheral IgM+ B cells, secretes a major proportion of the IgM antibodies occurring naturally in serum. Ly-1 B cells also seed a large number of IgA+ plasma cells to the gut walls, thereby contributing significantly to production of natural IgA antibodies in response to chronic stimulation by the normal gut flora. Apart from these naturally-produced antibodies, Ly-1 B cells also produce specific antibodies following deliberate immunisation with the bacterial cell wall antigens, phosphorylcholine and dextran. The inability of the X-linked immunodeficient CBA/N mice to produce antibody responses to these two antigens is overcome by reconstitution with normal Ly-1 B cells from the parental CBA strain. Ly-1 B cells therefore appear to play a dominant role in natural immunity and protection against bacterial infections. The compartmentalisation of development and function within murine B cells is suggestive of an evolutionary structuring of the murine immune system, with Ly-1 B cells representing a conserved, primitive B cell lineage and retaining key, associated functions.

B lymphocyte subsets in Hashimoto's thyroiditis

Two B lymphocyte subsets are identified on the basis of possession or lack of a surface molecule, CD5. The CD5+ B lymphocytes synthesize autoantibodies and in the process rearrange proximal variables of immunoglobulin genes. We have here studied the proportion and absolute counts of CD5+ B lymphocytes in the peripheral blood of 31 patients with Hashimoto's thyroiditis and related the findings to their HLA phenotypes and clinical features. Although the percentage and absolute number of surface immunoglobulin-positive (B) lymphocytes was comparable in patients to those in twenty controls, % CD5+ was significantly higher in the patient group (38.1 +/- 11.6 [+/- S.D.] vs. 27.9 +/- 10.1, p = 0.009). The absolute CD5+ cells (microliters) were also higher in patients with Hashimoto's thyroiditis (77.90 +/- 37.50 vs. 55.1 +/- 29.8, p = 0.020). The proportion of CD5+ cells was even higher in HLA-DR3 positive patients (43.1% +/- 7.2, n = 13) compared to six DR3+ controls (26.17% +/- 9.7, p = 0.0005). The difference between DR3- patients and controls was not significant (28.6% +/- 10.5 vs. 34.4% +/- 13.0). As the CD5 molecule may be induced on activated B lymphocytes, this study suggests that Hashimoto's thyroiditis is associated with an increase of activated B lymphocytes engaged in autoantibody synthesis. This defect is particularly obvious in DR3+ patients.