Anti‐IgM treatment influences immunoglobulin heavy and light chain mRNA levels in mitogen‐stimulated B lymphocytes

The mechanism by which soluble anti‐IgM inhibits plaque formation by lipopolysac‐charide‐stimulated B cells was investigated. Since lower amounts of immunoprecipitable μ heavy and ϰ light chains were found in cell lysates, this indicated that soluble anti‐IgM was inhibiting not only secretion. Subsequently, Northern blot analysis of poly(A⁺) RNA showed that the steady state levels of mRNA for immunoglobulin heavy and light chain from B cells stimulated with lipopolysaccharide were reduced if the cultures were treated with soluble anti‐IgM. The steady‐state levels of class I major histocompatibility complex antigen RNA were unaffected by anti‐IgM treatment. Addition of supernatants from mouse spleen cells stimulated with concanavalin A at day 2 of culture partially reversed the effect of soluble anti‐IgM on immunoglobulin expression.