Immunoglobulin µ and γ heavy chain classes are not determined by class-specific RNA-splicing enzymes

Abstract

An immunoglobulin (Ig)-producing lymphocyte can sometimes express one heavy-chain variable (V_H) region combined with different heavy-chain constant (C_H) regions. For example, single cells making IgM and IgD with the same antibody specificity have been observed¹. Cells, both singly² and in mass culture^3,4, switch from IgM to IgG production, and it is believed that the variable regions expressed are the same before and after the switch. We describe here the analysis of a hybrid derived by fusing an IgM-producing cell with an IgG producer, where the corresponding μ, and γ heavy chains bear different variable regions, denoted V₁ and V₂. This hybrid makes only the parental heavy chains—V₁C_μ and V₂C_γ—and not the novel combination V₂C_μ. This result suggests that the μ and γ heavy-chain classes are not determined by classspecific RNA processing.