Serum concentrations of IgM, IgG1, IgG2b, IgG3 and IgA in C57BL/6 mice and their congenics at the nu(nude)locus.

The absolute concentrations of IgM, IgG1, IgG2b, IgG3 and IgA were determined in mice of C57BL/6 background, from weaning to one year of age, by quantitative isotype-specific, indirect double sandwich ELISAs. The comparison of 10-40 weeks-old athymic nude C57BL/6 females with age matched females of the wild strain showed a general decrease of the whole serum Ig levels in the athymic mice, which was however contributed quite differently by the different Ig isotypes: a significant decrease (about 3.5 fold) was found for IgG2b only (0.34 mg/ml), whereas 1.5 fold more IgM (0.28 mg/ml) and about 2 fold more IgG3 (0.27 mg/ml) were detected, the IgG1 (0.19 mg/ml) and IgA (0.07 mg/ml) levels remaining within the normal range ! Limited data for IgG2a suggest that that this isotype may also be decreased in nude mice (0.36 mg/ml) in comparison with normal B6 + mice (0.54 mg/ml). Thus, although homozygosity at the nu locus results in a lack of effector T cells, our data show, at the humoral level, a limited degree of thymus dependence of an Ig isotype. It is intriguing that, although thymus dependence of several Ig isotypes looked evident ten years ago in early studies on nude mice, more recent data are very variable and controversial in this respect.