Abstract
Background. Severe malnutrition is the main cause of immunodeficiency in children under five years old in areas of economic depression in developing countries, and it is associated with generalized atrophy of lymphoid tissues. Urtica dioica L. is a medicinal herb with multiple pharmacological functions; it acts as modulator of the immune response, stimulating the proliferation of T lymphocytes in vitro.
Objective: To determine the ability of U. dioica L. to modulate the immune response of malnourished rats in the first 21 days of life.
Methods: Third-degree malnutrition during lactation was induced by food competition, and treatment with U. dioica L was tested. Day-old Wistar rats were randomly assigned to three groups: a) the well-nourished group, b) the untreated malnourished group and c) the malnourished group treated with 0.2 g/mL U. dioica L. on days 14, 16, 18 and 20. On day 21, animals were euthanized, and the thymus, spleen, bone marrow and blood were obtained. Lymphocyte subpopulations were determined in the thymus and leukocyte subpopulations in blood. The total number of nucleated bone marrow cells was determined, and the proliferative capability of spleen lymphocytes from malnourished rats treated with U. dioica L. was compared to that of other groups.
Results: U. dioica L. decreased CD4-CD8- lymphocytes and increased CD4+CD8+ lymphocytes in the thymus, while in the blood, it increased CD4+ cells, monocytes and total T lymphocytes. The proliferation of spleen cells was stimulated in the malnourished rats, and a decrease in total nucleated bone marrow cells was observed. An increase in the red blood cell count, hemoglobin and white blood cell count was observed in malnourished rats treated with Urtica dioica L. (p≤0.05).
Conclusion: U. dioica L. had immunomodulatory effects since it promoted the differentiation of CD4-CD8- T lymphocytes towards CD4+CD8+ T lymphocytes and counteracted anemia and leucopenia associated with severe malnutrition.

Key words: Severe malnutrition, immunodeficiency, immunomodulatory activity, T lymphocytes, Urtica dioica L.