Incomplete block of B cell development and immunoglobulin production in mice carrying the ? MT mutation on the BALB/c background

Abstract

The expression of the preB cell receptor (preBCR), composed of the μ chain, surrogate light chains and the Igα /Igβ signal transduction unit, permits further differentiation of Bcell precursors. C57BL/6 mice homozygous for an inactivating mutation of the membrane exon of the μ chain gene (C57BL/6^{μ MT/μ MT}) cannot form a preBCR and are, consequently, devoid of mature B lymphocytes. Here we present evidence that the block of B cell development by the μ MT mutation is incomplete in BALB/c mice. Unlike C57BL/6^{μ MT/μ MT}, BALB/c^{μ MT/μ MT} mice generate small numbers of mature B cells, accumulate plasma cells and produce high levels of all immunoglobulin isotypes, except IgM. The observed phenomenon seems to be controlled by a single genetic locus that is not linked to IgH.