An Evolutionarily-Conserved Role for Murine Ly-1 B Cells in Protection Against Bacterial Infections

Abstract

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-I 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.

Key Words:

• Ly-1 B cells
• B cell lineages
• natural antibodies
• anti-bacterial antibodies
• IgA
• natural immunity