Analysis on the expression of protection to Listeria monocytogenes by MCF derived from T cells with a low thymus dependency

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So-called cell-mediated immunity has been regarded as a thymus-dependent immunity, however, there are various immune responses which can be easily mounted in neonatally thymectomized (NTx) mice but not in nude mice. Protective immunity to Listeria monocytogenes is an example of such an immunity with a low thymus dependency.In the present study, the characterization of protective T cells against L.monocytogenes, which are of low thymus dependency, was done. Among various lymphokins produced by Listeria-immune T cells, MCF was of the special interest in this study, since the biological significance of this lymphokine in the expression of protection has not yet been elucidated. T cells obtained from NTx mice immunized with viable L.monocytogenes was shown to be Lytl^+,L3T4^+ and Lyt2^- cells. The effector T cells could release several lymphokines upon stimulation with specific antigen; however, they showed an impaired release of IL-2 and antigen-specific proliferation. It was suggested th … More at the characetristics of T cells with a low thymus dependency may be a low requirement for clonal expansion. Using the culture supernatant of Listeriaimmune T cells plus antigen, a partial purification of MCF was carried out by a gel chromatography. Fractions showing MCF activity but no contaminating MAF activity could be obtained. When this MCF fraction was injected into mice, a marked accumulation of macrphages was observed 10 h after injection. MCF-induced accumulation of macrophages was effective against challenge with relatively small dose of virulent strain and with even a high dose of low virulent strain of L.monocytogenes. The most significant level of protection was observed in the footpad given MCF, probably because of the localization of MCF at this site. When IFN-<gamma> was used as MAF in vivo, the highest level of protection was obtained by the use of an additional administration of MCF. These results suggested that MCF, which is produced by T cells with a low thymus dependency, plays an important role by itself in the expression of protective immunity and also is capable of showing the synergistic effect with MAF/IFN-<gamma>. Less