The injection into newborn rabbits of a small quantity of human albumin, associated with red blood corpuscles or nucleated rabbit cells, induces an antibody response in the majority of animals, whereas the same quantity of antigen in solution fails to stimulate antibody formation or induces tolerance. The promoting capacity of the cells depends on attachment of antigen to them.
The antibody produced after the injection of albumin, associated with nucleated cells, is of recipient origin. However, immunoglobulin carrying the marker of donor cells can be demonstrated in the recipient animals, and may reach serum concentrations similar to those normally present in animals which are heterozygous with respect to the marker. It appears that the antibody-promoting function and the synthetic capacity for allotype are quite distinct and that the period required for allotype formation is very short with mononuclear peritoneal exudate cells and is very much longer with cells from the thymus. The capacity of cells from lymph nodes for sustained allotype formation is less than that of thymus cells but greater than that of mononuclear peritoneal exudate cells.