Mycopathologia 124: 189-194, 1993. 1993 KluwerAcademic Publishers. Printedin the Netherlands. Immunosuppressive effects of aflatoxin in growing rats S. Raisuddin, 1 K.P. Singh, 2 S.I.A. Zaidi, 3 B.N. Paul 2 & P.K. Ray 1 aBose Institute, P-1/12, CIT Scheme VII-M, Calcutta, 700 054 India; 2Industrial Toxicology Research Centre, Mahatma Gandhi Marg, Lucknow, 226 001 India; SDepartment of Dermatology, Veterans Administration Medical Centre, Cleveland, OH 44106, USA Received 11 August 1992; acceptedin revised form 4 August 1993 Abstract. The immunosuppressive potential 'of aflatoxin B1 (AFB1), the carcinogenic metabolite of Aspergillus flavus, was evaluated in growing rats. The weanling rats were subchronically exposed to 60, 300 and 600 Ixg AFBJkg body weight for four weeks on alternate days by oral feeding. Various parameters of cell mediated immunity (CMI) and humoral immunity were assessed in control and treated animals. CMI was evaluated by measuring delayed type of hypersensitivity (DTH) response and humoral by plaque forming cell (PFC) assay. The lymphoproliferative response assay for T- and B-cells was also performed. It was observed that AFB1 selectively suppressed cell mediated immunity in growing rats. AFB1 suppressed CMI at the 300 and 600 p~g dose levels only as measured by DTH response assay. It is concluded that continuous low level exposure of aflatoxin to growing host may enhance its susceptibility to infection and tumorigenesis. Key words:Aflatoxin B1, Cellular immunity, Immunosuppression, Weanling rats Abbreviations: AF - Aflatoxin; AFB~ - Aflatoxin B1; CMI - Cell mediated immunity; CPM - Counts per minute; DTH - Delayed type of hypersensitivity; GST - Glutathione-S-transferase; LPS - Lipopoly- saccharide; PFC - Plaque forming cell; PHA - Phytohemagglutinin; SRBC - Sheep red blood cells Introduction In recent years some attention has been paid to evaluate toxic effects of aflatoxin (AF) in the developing host [1]. This has happened for two main reasons: (1) in utero exposure of aflatoxins to animals and humans has been reported [2-4], and (2) aflatoxin exposure to a developing host may take place through mother's milk [5, 6]. The presence of aflatoxins has been reported in mar- keted milk samples from several countries [7]. The contaminated milk is often consumed by growing individuals both in developed and de- veloping countries. A developing host exposed to aflatoxins under such situations may be more susceptible to its toxicity compared to an adult. In particular, the probable disruption of biochemical and immunological defence mechanisms may lead to greater susceptibility to toxic chemical ex- posure and infections. Some attempts have been made by us to inves- tigate immunotoxic responses of aflatoxin both in adult and growing animals [1, 8, 9]. Our studies on weanling rats showed that aflatoxin B1 (AFB1) induced lymphoid cell toxicity [1]. We found that macrophage function, a non-specific defence me- chanism, was disrupted as a result of AFB1 ex- posure to weanling rats. Besides macrophages, AFB~ affected the bone marrow cell population and spleen and thymus cellularity. Furthermore,