Normal lymphocyte transfer reaction in humans and its possible mechanism

This study illustrates the development of the skin reaction in human recipients to injected allogeneic lymphocytes from two aspects: the capacity of lymphocytes to elicit the reaction, and the ability of the recipient to react. The reaction is expressed by local skin induration and is biphasic. The first phase seems to be a hostgraft reaction; the second may require proliferation of graft cells as well as the reaction of host cells. Circulating fetal lymphocytes collected from a 12-week human embryo caused no reaction in an adult recipient; those from a 15-week embryo usually caused the first phase, with little or no second phase reaction, while those from 22- and 30-week fetuses and from a mature infant caused a normal, biphasic reaction. So, usually, did 22-week splenic lymphocytes, but fetal thymic lymphocytes usually provoked no reaction in adults. In premature infants given adult cells either both phases or the second were reduced; in normal infants the second response may be reduced but after six years of age the reaction is like that seen in adults.