Increased lymphocyte load of postcapillary venules in regional lymph nodes following stimulation with antigen -- isologous antibody complexes as compared with antigen alone.

In an attempt to study changing patterns of lymphocyte influx from blood into lymph nodes following regional antigenic stimulation, mice were injected with either fluid tetanus toxoid alone or complexed (at equivalence) with isologous antibody. The mean number of lymphocytes inside the basement membrane of cross-sectioned postcapillary venules (PCV) was evaluated as a function of time after antigen injection. 'Lymphocyte load' of PCV (LL/PCV) began to increase within less than a day after antigenic stimulation. The initial increment of LL/PCV values in both primary and secondary responses was greater when complexed rather than fluid antigen was used. Peak values were reached earlier, i.e., at the end of day 2, in presensitized as compared with unprimed animals (day 4). Maximum values of mean LL/PCV did not reflect the magnitude of subsequent antibody production under all experimental conditions. We conclude that changes in the LL/PCV belong to early lymph node reactions following regional antigenic stimulation. The pattern of this particular response may vary according to the type of immunizing agent used and the state of immunity (sensitization) of the animal as well as other factors still to be elucidated.