Influence of short-term protein malnutrition of mice on the phenotype and costimulatory signals of lymphocytes from spleen and Peyer’s patches

The objective of this study was to investigate the impact of short-term protein malnutrition (PM) on immunoglobulin A (IgA) production and on the number and phenotype of lymphocytes in Peyer’s patches (PP) and in the spleen. Balb/c mice were fed for 4, 7, or 10 d with a protein-deficient diet (0.1% protein). We determined B lymphocytes (CD40+), T lymphocytes (CD3+), T-helper (CD4+), and T-suppressor (CD8+) cells and the expression of costimulatory signals B7.1 (CD80) and B7.2 (CD86) on B cells and their counter receptors CD28 and CTLA-4 on T cells by fluorescence-activated cell-sorting analysis. Luminal IgA concentration in the small intestine was determined by an enzyme-linked immunosorbent assay. Four days of PM caused a significant reduction in the number of mononuclear cells in the spleen (5.6 × 107 ± 1 × 107 versus 2.4 × 107 ± 0.5 × 107, P < 0.001) and the PP (13 × 106 ± 3 × 106 versus 8.6 × 106 ± 2 × 106, P < 0.01). There was a relative increase of T cells in the spleen and a relative increase of B cells in the PP. Luminal IgA content of small intestine was significantly reduced after 4 d of PM (242 ± 55 μg versus 173 ± 39 μg, P < 0.05) and remained at about this level until day 10 of PM. Four days after PM, the costimulatory signals B7.1 and B7.2 on B cells were upregulated in the PP but markedly downregulated in the spleen, which was inversely related to the expression of the counter receptor CD28 on T-helper cells. We conclude that short-term PM increases the activation of B cells in the PP but reduces the relative number and activation state of splenic B cells. Only 4 d of PM caused a systemic and intestinal immunodepression, as indicated by a markedly decreased content of mononuclear cells in the PP and the spleen.