The CD4/CD8 ratio in the blood does not reflect the response of this index in secondary lymphoid organs of weanling mice in models of protein-energy malnutrition known to depress thymus-dependent immunity.

A low ratio of cellular numbers within CD4+ (helper/inducer) relative to CD8+ (suppressor/cytotoxic) thymic lymphocyte subsets (low CD4/CD8 ratio) is widely accepted as fundamental to the depression in thymus-dependent immunocompetence associated with wasting protein-energy malnutrition (PEM). The objective of this investigation, therefore was to determine the CD4/CD8 ratio in peripheral lymphoid compartments of diverse murine models of protein-energy malnutrition which produce systemic wasting (loss of approximately 1.8% of initial body weight per day), lymphoid involution and (as shown in many previous studies) depression in thymus-dependent immunocompetence. In the first of two experiments, male and female weanling mice of disparate inbred strains, CBA/J and C57BL/6J, were allocated to a zero-time control group (23- and 19-d-old, respectively), or to groups fed for 14 d as follows: ad libitum intake of a complete purified diet (19% crude protein, 17 kJ/g gross energy), restricted intake of the complete diet, or ad libitum intake of an isocaloric low protein diet (0.6% crude protein). In a supplementary experiment, (0.6% crude protein). In a supplementary experiment, male and female C57BL/6J weanling mice were fed the complete diet or the low protein diet for either 6 or 21 d. CD4+ and CD8+ thymic lymphocytes were enumerated by flow cytometry in mononuclear cell suspensions from blood, spleen and mesenteric lymph nodes. A low CD4/CD8 ratio is common in the blood in wasting protein-energy malnutrition, but appears uncharacteristic of the profoundly involuted lymphoid organs which generate acquired immune responses. The CD4/CD8 ratio is irrelevant to the thymus-dependent immunoincompetence previously demonstrated in the rodent models used in this investigation.