Subacute Immunotoxicity Study of Formaldehyde in Male Rats

Immune functions were examined in male rats following 28 day oral administration of formaldehyde by gastric tube at dose levels of 0, 20, 40, and 80 mg/kg. Routine parameters examined included hematology, clinical chemistry, and body, thymus, kidney, and liver weights. In addition, cellularity of spleen and lymph nodes, histology of spleen, thymus, lymph nodes, liver, kidney, small and large intestines, and histochemistry of spleen and lymph nodes were evaluated.Immune parameters evaluated included serum hemagglutinin antibody response; antibody plaque forming cell response to sheep erythrocytes (lymphocyte-dependent antigen); microbicidal activity of Candida albicans; and phagocytic activity by adhesion of microspheric hydrophylic synthetic particles to leukocyte cell membrane.Body weights were slightly decreased at high dose level (80 mg/kg). The difference was significant when compared to the controls. The lymph node weights were significantly increased in rats receiving formaldehyde. The cellularity of lymphoid organs was not influenced after 28 day exposure to formaldehyde.Oral administration of formaldehyde to rats resulted in dose-dependent reduction of antibody responses (IgG + IgM) at doses of 20, 40, and 80 mg/kg.However, there was no significant reduction of the spleen cells producing IgM antibodies in exposed rats. With the exception of the activity of PMN + monocytes, the microbicidal activity of cells which phagocytized Candida albicans and phagocytic activity of blood leukocyte cells were not significantly decreased. In comparison to controls, the hepatocytes of the exposed animals had increased cytoplasmic vacuolization. Histochemistry revealed narrowing of the thymus-dependent zone in the spleen. In addition, channels across the marginal zone were frequently observed. These channels probably allow direct migration of lymphocytes from the thymus dependent zone into the red pulp spleen.