Quantitative aspects of the nonspecific humoral immune response to sheep erythrocytes

The kinetics and magnitude of the nonspecific humoral immune response was studied at the cellular level in mice immunized with sheep erythrocytes (SRBC). Intravenous injection of the antigen evoked, in addition to a specific anti-SRBC response, a nonspecific response of all immunoglobulin (Ig) classes and subclasses. This nonspecific response peaked on day 4 or 5 after immunization, irrespective of the Ig class. The absolute number of nonspecific Ig-secreting cells induced by immunization varied with the different Ig-classes, and it was not proportional to the background level of Ig-secreting cells of the various classes. The nonspecific IgM-IgG1- and IgG2-response was 3 to 4 times as large as the antigen-specific responses of these classes. The nonspecific IgA-response, however, was many times greater.