THE PASSIVE TRANSFER OF ACQUIRED RESISTANCE TO LISTERIA MONOCYTOGENES.

Five methods have been used in an effort to reveal an antibody that could account for the features of acquired resistance to Listeria monocytogenes: (a) a comparison of the growth rates of Listeria in the spleens of mice infused repeatedly with normal or immune mouse serum; (b) measurement of peritoneal clearance of Listeria in the presence of normal or immune mouse serum; (c) the survival rate of Listeria in monolayers of mouse macrophages infected in the presence of normal or immune mouse serum; (d) the effect of injecting urea extracts of spleens and peritoneal macrophages of normal or immune mice on the survival and growth of Listeria in recipient animals; (e) a comparison of survival rates in lethally infected mice following the passive transfer of cells and serum from normal or immune donors. The only evidence of passive protection was obtained when intact living cells from immune donors were used for transfer under conditions which permitted them to interact with the parasite population.