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Nutritional Immunology

Zinc Deficiency Suppresses the Development of Oral Tolerance in Rats¹

Istituto Nazionale di Ricerca per gli Alimenti e la Nutrizione, 00178 Roma, Italy and ^* Università degli Studi della Tuscia, Dipartimento Scienze Ambientali, 01100 Viterbo, Italy

³To whom correspondence should be addressed. E-mail: mengheri{at}inran.it.

Oral tolerance is a specific immune unresponsiveness to food antigens to prevent hypersensitivity reactions. We investigated whether zinc deficiency affects oral tolerance. Rats were fed a control (C) or zinc-deficient (ZD) diet, or pair-fed (PF) to ZD rats for 28 d. Beginning on d 7, rats were administered ovalbumin (OVA) orally to induce tolerance, or PBS 3 times/wk, and were then immunized by OVA injection. The proliferation of mesenteric lymph node (MLN) and spleen lymphocytes after in vitro OVA stimulation and the delayed-type hypersensitivity were higher in OVA-fed ZD than in OVA-fed C rats and not different between OVA- and PBS-fed ZD rats, indicating a suppression of tolerance. Lymphocyte proliferation did not differ between PF and C rats. Expressions of cytokines involved in oral tolerance, i.e., interleukin (IL)-4, IL-10 and transforming growth factor-ß, were higher in OVA- than in PBS-fed C rats, but not in ZD rats. Apoptosis was higher in OVA- than in PBS-fed C rats but not different between OVA- and PBS-fed ZD rats. Inflammation and ulcerations that were not present in ZD rats on d 7 (ZD₇) developed in OVA- or PBS-fed ZD rats. Compared with ZD₇ rats, tumor necrosis factor- and cytokine-induced neutrophil chemoattractant were higher in OVA- and PBS-fed ZD rats, whereas interferon- increased only in OVA-fed ZD rats. In conclusion, zinc deficiency suppresses oral tolerance through dysregulation of cytokine expression and lack of antigen-specific clonal deletion. We suggest that abrogation of tolerance may lead to development of mucosal inflammation and damage.

KEY WORDS: • zinc deficiency • oral tolerance • intestine • cytokines • rats

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