Effect of anti‐γ3 antibodies on immunoglobulin isotype expression in lipopolysaccharide‐stimulated cultures of mouse spleen cells

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Abstract
To test the hypothesis that γ3 is the pivotal isotype for sequential heavy chain switching from μ to each of the γ isotypes, we have compared the effects of anti‐γ3 and anti‐μ antibodies on the expression of immunoglobulin isotypes in lipopolysaccharide (LPS)‐stimulated cultures of mouse spleen cells. IgM‐, IgG1‐, IgG2b‐ and IgG2a‐containing plasma cells were enumerated by immunofluorescence and secreted immunoglobulins were measured by radioimmunoassay. Although anti‐γ3 and anti‐μ, were equally effective in inhibiting the LPS‐induced differentiation of IgG3 plasma cells, anti‐γ3 had no effect on the differentiation of IgM, IgG1, IgG2b, or IgG2a plasma cells. These results support a direct mechanism of heavy chain immunoglobulin switching.