Demonstration of serum alpha1-macroglobulin on leucocyte surfaces in non-pregnant and pregnant rats.

alpha1-macroglobulin (alpha1-M) was demonstrated by indirect immunofluorescence staining on the surface membrane of leucocytes obtained from rat blood and lymphoid tissue. The incidence of alpha1-M positive cells correlated with serum levels of the protein. Compared with blood, a significantly higher percentage of staining cells was demonstrated in spleen and lumbar lymph nodes. During pregnancy, when serum levels of alpha1-M were significantly elevated, the proportion of alpha1-M staining leucocytes increased in blood, Thymus and lymph nodes but the incidence of alpha1-M positive spleen cells was unaffected. The comparatively low incidence of alpha1-M staining thymocytes, together with the presence of alpha1-M on glass-adherent cells and on leucocytes from congenitally athymic rats, suggest that this protein is associated predominantly with B cells and monocytes.