Class- and subclass-specific antibody response to hemocyanin in nonmalignant paraproteinemia.

IgM, IgG, and IgA class-specific, as well as IgG subclass-specific antibody titers against the primary immunogen HPH were measured with ELISA in 19 patients with nonmalignant paraproteinemia (eight with IgG1, two with IgG2, two with IgG4, four with IgM, and three with IgA) and in a simultaneously studied age- and sex-matched control group. After primary immunization only IgM and IgA anti-HPH titers were significantly lower in the patient group. Four patients with relatively high IgG or IgA serum paraprotein levels did not produce antibodies in some Ig classes or IgG subclasses, whereas all other patients and all controls developed antibody titers in all classes and IgG subclasses. Low or absent antibody titers did not occur preferentially in the Ig (sub)classes to which the paraproteins belonged. After secondary immunization the patients could not increase or maintain their antibody titers as well as the controls, and this was most clear in the IgM and IgA antibody class. A direct correlation between polyclonal serum IgM levels and IgM anti-HPH titers was present in the patients. Such a correlation was absent for IgA in the patients and for all classes in the controls. It is concluded that humoral immunosuppression as measured with a newly encountered antigen in patients with nonmalignant paraproteinemia is most clearly expressed in the IgM and IgA antibody class and that the paraprotein (sub)class is not preferentially involved.