The lymphoid system and experimental neoplasias.

In the last decade or so immunologists have left the test tubes in which their serological mysteries were enacted and turned to consider the cells which are involved in immune responses. The resultant cellular immunologists have made discoveries which ought to have lent precision to the quite old notion that the immune mechanism is part of the natural defence system which, in vertebrates, can operate against malignant cells. I intend first to summarize some of the salient findings of the cellular immunolo-gists and secondly to consider a few examples of experimental interaction between the new-look lymphoid system and neoplastic cell populations. The lymphocyte not very many years ago was thought of either as a cell of astonishing philopro-genitive versatility or a dull cell with some un-specified part to play in immune responses. In either instance it was commonly supposed that lympho-cytes were produced in lymph nodes. This supposition rested on the apparently common sense attitude of, 'where else?'. The experiments of Gowans in the late fifties and early sixties provided the evidence which disposed of some of these misconceptions (Gowans, 1959). Gowans established that at least some lymphocytes were relatively long-lived re-circulating cells which could leave the blood stream via postcapillary venules in lymph nodes and return to it via the efferent lymphatics. It seemed that if indeed lymphocytes were produced in lymph nodes it was in relatively small quantities over a long period of time at least in the adult rodent. Jankovic, 1962) all independently showed that the thymus regulated the development of some aspects of immunological responsiveness in young rodents. In mice the ability to reject skin and tumour homo-grafts in particular was grossly impaired by neonatal thymectomy (Miller, 1961; Martinez, Dalmasso, and Good, 1962b). Further, many although not all, humoral immune responses were reduced by the same device; the particular deficit was in relation to the capacity to produce 7S antibody (Taylor and Wortis, 1968). In birds homograft rejection was also diminished by early thymectomy but humoral immunity was not affected (Warner and Szenberg, 1962). By contrast, removal of the bursa of Fabricius left homograft reactivity intact but led to failure to respond to antigenic stimulus by production of serum antibodies (Papermaster, Friedman, and Good, 1962b). These findings, taken in conjunction with the studies of the transplantation immunolo-gists, led to consolidation of the concept of two modes of immunity, humoral and cellular, which were not only different …