| Abstract: | The characteristics of the mononuclear phagocytes mediating resistance to infection with Listeria during the early phase (0 to 48 h) of the response have been investigated in genetically determined susceptible (A/J) and resistant (C57BL/6, B10.A/SgSn) strains of mice. Irradiation immediately before infection profoundly enhanced the bacterial growth in the resistant strain, while having no effect in the susceptible strain, over a wide range (3 x 10(3) to 10(5)) of infective doses. This effect of irradiation is demonstrable at low-dose radiation (200 roentgens) and can be reversed by repopulation with 20 x 10(6) syngeneic nucleated bone marrow cells. Administration of dextran sulfate 500 24 h before infection profoundly enhanced the bacterial growth in the susceptible strain, while having much less effect in the resistant strain. Thus, the genetic advantage of the resistant mouse strains to listerial infection, at least during the early phase of the response, appears to be due to a cellular mechanism that is highly radiosensitive and relatively insensitive to dextran sulfate 500. In the susceptible strain, the early protective cellular mechanism is radioresistant and highly dextran sulfate 500 sensitive. |
