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The CD45RA⁺ (Quiescent) Cellular Phenotype Is Overabundant Relative to the CD45RA^- Phenotype within the Involuted Splenic T Cell Population of Weanling Mice Subjected to Wasting Protein-Energy Malnutrition^1,2,

Department of Nutritional Sciences, University of Guelph, Guelph, Ontario N1G 2W1, Canada

The objective of this investigation was to determine whether an imbalance between naive- and memory-phenotype cells occurs within CD4⁺ and/or CD8⁺ splenic T cell subsets in models of protein-energy malnutrition (PEM) which produce wasting disease (loss of 1.6% of body weight per day for 14 d) and profound depression in thymus-dependent immunity. Male and female weanling mice of disparate inbred strains, CBA/J and C57BL/6J, were allocated to the following groups: zero-time control (23 d old and 19 d old, respectively), ad libitum intake of a complete purified diet (19% crude protein, 17 kJ/g gross energy), restricted intake of the complete diet, and (C57BL/6J, only) ad libitum intake of an isocaloric low protein diet (0.6% crude protein). Surface expression of isoforms of CD45, a component of the T cell receptor complex, as well as of the accessory molecule, CD2, were assessed by flow cytometry of splenic mononuclear cell suspensions. Both major T cell subsets in the malnourished groups contained a significantly higher proportion of cells expressing the surface marker, CD45RA, than was found in the spleen cells of the control groups. CD45RA⁺ (naive-phenotype) T cells represent the extreme of quiescence and stringent activation requirements among thymic lymphocytes. The results provide the first clear evidence of a T cell subset imbalance in PEM which is consistent with depression in acquired immunity and which occurs, apart from antigenic challenge, in a site wherein immune responses take place. The T cell receptor complex may emerge as a focal point of the depressive influence of PEM on the competence of thymic lymphocytes.

KEY WORDS: • mice • lymphocyte • protein-energy malnutrition • immunity • spleen

¹ Supported by individual operating grants to B. D. W. from the Natural Sciences and Engineering Research Council (NSERC) of Canada and the Nutricia Research Foundation (Holland) and by a NSERC of Canada Undergraduate Student Scholarship awarded to K. D. B.

² The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

³ To whom correspondence should be addressed.

Manuscript received 17 January 1995. Revision accepted 22 May 1995.