Humoral Antibody Responses in the Gar, <em>Lepisosteus osseus</em>.

Lepisosteus osseus possesses high titres of natural agglutinins to human group A (HuA) erythrocytes and to Salmonella typhosa &#39;O&#39; (STO) antigens. Moderate natural haemagglutinin titres to sheep red blood cells (SRBC) were noted. Cold agglutinin (4&#176;) titres exceeded agglutinin titres recorded at 25&#176;. Immunization with STO antigen resulted in a marked increase in corresponding anti-STO agglutinins, as well as increases in anti-HuA and anti-SRBC agglutinins. Animals immunized with SRBC antigen produced elevated anti-SRBC agglutinin titres, while immunization with HuA erythrocytes produced no changes in agglutinin levels. Immunization with STO following previous injections with HuA resulted in increases of corresponding anti-STO agglutinins, as well as marked increases in anti-HuA agglutinins. Absorption studies indicated that anti-STO agglutinins were not cross reactive against HuA antigens. Natural and immune antibodies were all of the same macromolecular class. Rises in antibody titres were reflected in both cold and warm agglutinins. Animals maintained for long periods at low temperatures exhibited preferential ability for increased synthesis of cold agglutinins to HuA. Natural haemolytic titres, as measured by an SRBC indicator system, were also elevated as compared to mammalian systems. These titres increased with stimulation with SRBC. Results suggest that the high levels of natural haemolytic and agglutinin activity in this species are of immunogenic origin. [ABSTRACT FROM AUTHOR]