Serum proteins and lymphoid tissues in germ-free mice fed a chemically defined, water soluble, low molecular weight diet.

Germ-free CFW mice reared on practical type steam sterilized solid diets showed lower than conventional levels of all serum immunoglobulins. Reared on water soluble, low molecular weight, chemically defined diets which had been sterilized by filtration, young adult germ-free mice demonstrated almost total absence of immune globulins. However, in older animals reared on this diet, a gradual increase with age, notably of IgG, became apparent. Total white blood cell count and differential counts were only slightly and not significantly lower in germ-free mice fed solid diet than in their conventional controls. Germ-free mice fed the water soluble diet, on the other hand, showed substantially lower white cell counts than the animals reared on solid diet. It is concluded that steam sterilized solid diet constitutes a major source of uncontrolled exogenous stimulation of the lymphoid tissues.