MECHANISMS OF RECOVERY FROM A GENERALIZED VIRAL INFECTION: MOUSEPOX : II. PASSIVE TRANSFER OF RECOVERY MECHANISMS WITH IMMUNE LYMPHOID CELLS

The following passive transfer experiments evaluated the contributions of the various host responses in recovery from mousepox. (a) Immune spleen cells transferred highly efficient antiviral activity, but preinfected recipients of these cells made no detectable splenic interferon or antibody in the 24 hr interval after cell transfer. (b) Passively administered interferon was ineffective. (c) Recipients of hyperimmune serum had much more antibody than recipients of immune spleen cells but significantly less antiviral activity. (d) Immune spleen cell populations with antiviral activity contained mediators of CMI to virus antigens. (e) The antiviral activity of immune spleen cells was specific; it was inhibited by in vitro treatment with ATS, anti-light chain serum, and anti-theta ascitic fluid, but not by removal of mononuclear phagocytes from the immune population. These results are interpreted to mean that recovery mechanisms conferred by immune spleen cells were triggered by specifically sensitized, thymus-derived lymphocytes, and that antibody and interferon responses were of less importance. A radiosensitive recipient component was necessary for the full expression of the antiviral activity of both immune cells and immune serum. It seemed likely that this component was the blood monocyte

MECHANISMS OF RECOVERY FROM A GENERALIZED VIRAL INFECTION: MOUSEPOX : I. THE EFFECTS OF ANTI-THYMOCYTE SERUM

Agglutination and immunofluorescence tests in vitro showed that the ATS used in these experiments cross-reacted with macrophages and RBC. However, ATS was not toxic in vivo, and small doses given subcutaneously depleted thymus-dependent areas of lymphoid tissues and selectively depressed blood lymphocyte counts without affecting other cell types in the blood. Furthermore, the function of littoral macrophages as indicated by the clearance of blood-borne virus and its subsequent behavior over a 48 hr period in the liver and spleen was not changed by ATS. Thus, the innate resistance of these vital target organs was not depressed. A similar regimen of subcutaneous ATS caused a highly significant increase in mortality from mousepox with an associated failure to control virus growth in the liver and spleen which was manifest by 6 days after infection. The interferon and neutralizing antibody responses were not impaired in ATS-treated mice, but the cell-mediated immune response was significantly suppressed. This evidence, and consideration of the timing of these host responses during the course of infection in relation to the control of virus growth in the liver and spleen, led to the conclusion that cell-mediated immunity probably contributed an essential acquired recovery mechanism. However, no evidence was obtained concerning the nature of this antiviral mechanism

MECHANISMS OF RECOVERY FROM A GENERALIZED VIRAL INFECTION: MOUSEPOX : III. REGRESSION OF INFECTIOUS FOCI

Histological and immunofluorescence techniques showed that mononuclear cells invaded virus-infected foci in the livers of passively immunized mice within 10 hr of the receipt of immune spleen cells or hyperimmune serum; by 24 hr, marked destruction of virus antigens had occurred in these lesions. Immune cell transfer promoted denser packing of mononuclear cells in the foci and more efficient destruction of infectious material than immune serum. Similar liver lesions developed by the 6th day after sublethal, primary, subcutaneous infection in normal mice. In contrast, in mice with GVHR which were immunosuppressed but possessed hyperactive macrophages and unimpaired splenic interferon response, mononuclear cells did not invade liver lesions and the animals died. These results, together with data reported previously, indicated that mononuclear cell invasion of infected liver foci, triggered by CMI, was of key importance in recovery from primary mousepox. The roles of specifically sensitized lymphocytes and macrophages within lesions were not directly evaluated, but indirect evidence suggested that lymphocytes could cause no more than a halt in virus multiplication, and that macrophages were required for the inactivation of preformed virions. Possible augmentation of the efficiency of macrophages by locally-produced lymphocyte interferon, neutralizing antibody, or stimulation of their phagocytic and intracellular digestive capacity cannot be excluded