The V kappa IIIb light chain sub-subgroup. II. Isotype expression in acquired hypogammaglobulinaemia and as a function of age.

The V kappa IIIb sub-subgroup of the human immunoglobulin V kappa III light chain subgroup has at least two unique properties. First, some IgM monoclonal autoantibodies, in particular cryoprecipitable anti-IgG (Kunkel et al., 1974; Ledford et al., 1983), anti-low density lipoprotein (Ledford et al., 1983) and certain cold agglutinin (Feizi et al., 1976) antibodies predominantly contain V kappa IIIb light chains. Second, in normal adult human serum, V kappa IIIb comprises approximately 25% of the IgM but less than 0.4% of the IgG or IgA kappa-chain pools (Moynihan, Looney & Abraham, 1985). Studies have suggested an altered regulation of IgM, IgG, and IgA-V kappa IIIb in some patients with acquired hypogammaglobulinaemia, a heterogeneous group of immunodeficiencies with low serum levels of Ig. An increase in the serum levels of V kappa IIIb light chains has been noted in some of these patients (Solomon & Mclaughlin, 1969) which is apparently due to elevated levels of light chains of the V kappa IIIb sub-subgroup (Greenstein & Abraham, 1984). However, the isotype association of V kappa IIIb in these patients has not been determined. In order to clarify whether the noted increase in V kappa IIIb levels is due to its selective expression with IgM or to an abnormality of immunoregulation, the heavy chain isotypes associated with V kappa IIIb light chains have been determined in a previously studied group of adults with acquired hypogammaglobulinaemia (Greenstein & Abraham, 1984). Further, the isotype distribution of V kappa IIIb light chains in another group of functional, albeit transient, hypogammaglobulinaemics (i.e. normal neonates) has also been studied by measuring IgM-V kappa IIIb levels in cord blood, and compared to the V kappa IIIb serum levels found in aged adults (mean age 75 years).