Crude transfer-factor preparations stimulate trypsinized human lymphocytes to form rosettes with sheep red cells.

The binding sites for sheep red cells (E) on human lymphocytes are trypsin-sensitive but regenerate in vitro on incubation at 37 degrees C. The rate of this regeneration was increased in the presence of dialysates of human leucocyte extracts (DLE). Thus incubation of trypsinized lymphocytes for 3 hr in appropriate dilutions of DLE resulted in a 2- to 6-fold increase of E-binding activity above that observed in medium-incubated control lymphocytes. Dialysates prepared from human thymus and brain similarly accelerated recovery of E-binding activity whilst dialysates of human fibroblasts and liver cells were inactive. The regeneration of trypsinized membrane immunoglobulin was slightly delayed in the presence of DLE. These findings indicate that leucocyte dialysates contain an activity which preferentially stimulates the regeneration of a T-lymphocyte membrane component. It is suggested that this activity may account for the immunological restoration observed in some patients with T-lymphocyte deficiency after injection of leucocyte dialysates.