Antibody isotypes in sera of equine fetuses aborted due to Leptospira interrogans serovar pomona-type kennewicki infection

Leptospira-specific antibody isotypes in sera of late term equine fetuses aborted due to Leptospira interrogans serovar pomona-type kennewicki infection were characterized and compared with those of their dams. IgM was the dominant Leptospira-Specific isotype in both fetuses and mares. However, IgGa was the isotype in highest concentration in petal sera and strong Leptospira-specific IgGa but no IgGb and little or no IgG(T) were detected. In contrast, although IgGb was quantitatively the dominant isotype in mares serum, Leptospira-specific serum IgG in aborting mares was dominated by IgG(T) but also included large amounts of IgGa and IgGb. IgGa and IgGb were quantitatively the dominant isotypes in sera of fetuses and mares, respectively. Affinity purified IgGa from fetuses did not agglutinate leptospires but serum devoid of IgGa did, suggesting that IgM is the principal agglutinating antibody. It is concluded that the equine fetus is deficient in IgGb and IgG(T) synthesis.