ONTOGENY OF MACROPHAGE RESISTANCE TO MOUSE HEPATITIS IN VIVO AND IN VITRO

Adult or weanling C3H mice were found to be genetically resistant to a strain of mouse hepatitis virus. Infant C3H mice, however, developed infection and died from mouse hepatitis virus when minimal infectious doses of virus were given to them. There was a delay in the time of death compared to that of the genetically susceptible strain, and the virus recovered from these mice had increased pathogenicity for C3H mice. The ontogeny of resistance to hepatitis in the C3H mice thus progresses from delayed susceptibility to complete resistance as the age of the host increases. It is reflected in increased resistance of macrophages derived in vitro from liver cultures of infant mice of different ages. This increase in resistance with age was reduced by maintaining the cultures for a longer period of time before inoculation, or by increasing the number of explants in a given culture. Resistant cells were uniformly furnished by mice age 16 days, or more. It is concluded that a process of maturation of resistance of the cells takes place after the mice are born, but that this does not continue under in vitro conditions, and that it may be modified by the environment of the cells

Indomethacin sensitizes resistant transformed cells to macrophage cytotoxicity

AbstractActivated macrophages are well known to exhibit anti-tumor properties. However, certain cell types show intrinsic resistance. Searching for a mechanism that could explain this phenomenon, we observed that the supernatant of resistant cells could confer resistance to otherwise sensitive tumor cells, suggesting the presence of a secreted suppressor factor. The effect was abolished upon dialysis, indicating that the suppressor factor has a low molecular weight. Further studies showed that prostaglandin E2 (PGE2) is secreted by the resistant tumor cells and that inhibition of PGE2 production by indomethacin, a cyclooxygenase (COX) inhibitor, eliminated the macrophage suppression factor from the supernatant, and sensitized the resistant tumor cells to macrophage cytotoxicity. This study emphasizes the important role of tumor-secreted PGE2 in escaping macrophage surveillance and justifies the use of COX inhibitors as an adjuvant for improving tumor immunotherapy

In vitro and in vivo studies of the properties and effects of antimacrophage sera (AMS)

Antimacrophage sera (AMS) were prepared in rabbits by injection of mouse peritoneal cells with or without purification by in vitro culturing. These AMS showed high cytotoxic activity against macrophages in culture. The antimacrophage sera were not specific for macrophages; they cross-reacted and were cytotoxic to lymphocytes and granulocytes in the in vitro assay. Injection of AMS into mice did not affect antiShigella antibody production, nor did it prolong skin allograft survival. Furthermore, AMS-treated macrophages did not lose their ability to induce antiShigella antibody production in irradiated mice. On the other hand, AMS inhibited phagocytosis of Bacillus subtilis by macrophages and likewise increased the synthesis of DNA in cultured macrophages

The role of macrophages in the induction of antibody in X-irradiated animals

A study was carried out on the function of macrophages in inducing antibody production to Shigella antigen, and on the effect of X-irradiation on the `immunogenic' function of macrophages. Peritoneal macrophages, which had been incubated with Shigella and then injected into mice exposed to 550 r, triggered the formation of agglutinating antibody in animals which did not respond to the injection of the antigen alone. The antibody formed was not produced by `contaminating' lymphocytes of the peritoneal exudate, since: (a) lymph node cells at doses higher than those of the macrophage inocula did not produce antibody when treated and injected under similar conditions, and (b) lymphocyte-free macrophage populations, obtained by culturing in vitro cells of peritoneal exudates, triggered the production of antibody when injected in to X-irradiated recipients after interaction with the antigen. Macrophages from irradiated donors incubated with Shigella were incapable of inducing antibody formation in X-irradiated mice. Animals exposed to higher doses of irradiation (900 r) did not produce antibody following injection of macrophage—antigen complexes. It was, therefore, concluded that macrophages from normal animals elicited the production of antibody by the lymphoid cells of the irradiated recipients

Effect of X-irradiation on various functions of murine macrophages

Unstimulated macrophages of X-irradiated mice have lost the capacity to induce an immune response to Shigella. Other studied functions of macrophages were unaffected or activated by X-irradiation. The phagocytic ability of irradiated macrophages, both in vivo and in vitro, was the same as that of normal cells. Irradiation of macrophage donors caused activation of several macrophage functions: DNA synthesis in irradiated macrophages was slightly higher, and RNA synthesis was six times higher than in non-irradiated controls. Choline uptake was significantly enhanced by irradiation. The levels of two lysosomal enzymes, acid phosphatase and cathepsin D, were elevated in macrophages taken from irradiated donors. The rate of particulate antigen (Shigella) degradation was slightly faster in irradiated macrophages, whereas no difference could be detected when soluble antigen ((T,G)-PRO--L) was employed

Studies on the binding and phagocytic inhibition properties of antimacrophage globulin (AMG)

Ring fluorescence of mouse macrophages, seen following incubation at 4° with rabbit anti-macrophage globulin (AMG) and fluorescein-conjugated goat—anti-rabbit globulin, was transformed into aggregate fluorescence after subsequent maintenance at 37°. Studies based on the saturation binding of radiolabelled AMG indicated that between 400,000 and 800,000 heterologous antigenic determinants are present on the macrophage surface. AMG and F(ab')(2) and Fab but not Fc fragments, could both bind to macrophages and inhibit phagocytosis; attachment of bacteria was, however, unaffected. Kinetic experiments based on the assumption that phagocytosis is analogous to carrier-mediated membrane transport indicated that non-competitive inhibition is responsible for AMG impairment of macrophage phagocytic capacity