The response of immunologically reconstituted mice to allogeneic skin or tumour grafts

A study has been made of cytological and histological changes in lymph nodes draining grafts of allogeneic skin or tumour. The two types of graft provoked mitosis of both thymus- and bone-marrow-derived lymphocytes; this activity was associated with reactive changes initially in the paracortex and then in germinal centrts and medullary cords. Grafts of allogeneic skin evoked two peaks of mitosis which declined rapidly as the graft was rejected. Transient mitotic activity also occurred in response to (control) syngeneic skin, coinciding with increased lymph-node weight and some paracortical hyperplasia but (cf. changes found after allografting), other parts of the node did not respond. Allogeneic EL4 lymphoma cells gave rise to a greater and more rapid immunological response than did skin grafting. The mitotic response to the injected tumour cells failed, at least in the draining lymph nodes, long before death of the host due to progressive tumour growth. It is suggested that both the greater mitotic response, and its later failure, are related to the progressive growth of the tumour and to the everincreasing antigenic burden which such a tumour represents.     

Maturation of reticular dendrites: loss of spines and development of bundles

Dendrite systems of most neurons in the brain stem reticular core undergo two significant changes between birth and maturity. The shaggy spinelike excrescences (heteromorphic protospines) which cover each dendrite and soma at birth, are lost completely, resulting in smooth, spineless reticular dendrites in the adult nervous system. It is suggested that these spinelike structures and their associated presynaptic terminals are concerned with primitive needs of the internal milieu and are replaced by a secondary system of terminals which provide substrate for more complex core functions. In contrast to the familiar radiative aspect of reticular dendrites in newborn organisms, dendrite shafts are rearranged into bundles which surround the fascicles of axons running longitudinally through the reticular formation. The bundles of dendrites are marked by closeness of apposition of the shafts and continuous change in the dendritic elements comprising them. On the basis of previous work, it is suggested that these bundles are the repository for central programs mediating certain stereotyped repetitive output patterns such as respiration and the rest-activity cycle.