Some results on an immunochemical analysis of fluorescein-conjugated antihuman IgM sera

Some fluorescein-conjugated antihuman IgM sera are capable of demonstrating IgM antibodies to toxoplasma present in infected newborns. Other comparable reagents to human IgM do not. This discrepancy was never observed when IgM toxoplasma antibodies from adult patients were studied. Immunochemical analysis demonstrated anti-IgM, reactive to newborn IgM toxoplasma antibody, to contain additional antibody specificity to μ chain in comparison with the nonreactive antiserum. In view of published findings that μ chain antigenic specificities are represented in each 19S IgM molecule and the high frequency of 7S IgM in newborns, it was tentatively concluded that the reactive anti-IgM serum demonstrates 7S IgM toxoplasma antibodies in the serum of newborns, these being of a μ chain antigenic specificity that is not detected by nonreactive antiserum.