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Mechanism of Altered B-Cell Response Induced by Changes in Dietary Protein Type in Mice¹

Gustavo Bounous, Nazih Shenouda^*, Patricia A. L. Kongshavn and Dennis G. Osmond^*

Department of Surgery, Centre Hospitalier Universitaire, Sherbrooke, Québec, Canada, J1H 5N4 ^* Department of Anatomy, McGill University, Montreal, Quebedc, Canada, H3A 2B2 Department of Physiology, McGill University, Montreal, Quebec, Canada, H3A 2B2

The effect of 20 g/100 g dietary lactalbumin (L) or casein (C) diets or a nonpurified (NP) diet on the immune responsiveness of C57Bl/6J, C3H/HeJ and BALB/cJ mice has been investigated by measuring the response to the T cell-independent antigen, TNP-Ficoll. To investigate the possible influence of dietary protein type on the supply of B lymphocytes, bone marrow lymphocyte production has been examined by a radioautographic assay of small lymphocyte renewal and an immunofluorescent stathmokinetic assay of pre-B cells and their proliferation. The humoral response of all mice fed the L diet was found to be higher than that of mice fed the C diet or nonpurified diet. A similar pattern of dietary protein effect in (CBA/N x DBA/2J) F₁ mice carrying the xid defect was observed following challenge with sheep red blood cells (SRBC). An even greater enhancing effect of dietary L was noted in normal (DBA/2J x CBA/N) F₁ mice after immunization with SRBC, but in contrast, the normal large-scale production of B lymphocytes in mouse bone marrow was independent of the type of dietary protein. Dietary protein type did not affect blood level of minerals and trace metals. The free plama amino acid profile essentially conformed to the amino acid composition of the ingested protein, suggesting that the changes in plasma amino acid profile might be a crucial factor in diet-dependent enhancement or depression of the B-cell response. The findings indicate that the observed effects of altered dietary protein type on humoral immune responsiveness are not exerted centrally on the rate of primary B-lymphocyte production in the bone marrow, but may reflect changes either in the functional responsiveness of the B lymphocytes themselves or in the processes leading to their activation and differentiation in the peripheral lymphoid tissues.

KEY WORDS: • diet • protein • immunity • B-cell response • mice

¹ Supported by grants from the Medical Research Council of Canada and from the National Cancer Institute of Canada.

Manuscript received 16 November 1984. Revision accepted 8 July 1985.