Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)


Medical Sciences


Dr. K.L. Rosenthal


These studies were undertaken to characterize cytotoxic cell responses to Pichinde virus (PV; a member of the arenavirus family) in various strains of inbred mice. Emphasis was placed on examining the relationship between cells with natural killer (NK) activity and H-2 restricted, virus-specific cytotoxic T lymphocytes (CTL) that are detected in the spleens of inbred mice after infection with PV.

Primary i.v. inoculation of mice with PV resulted in augmented spleen NK activity that peaked at 3- 4 days after infection. This NK response was followed by an H-2 restricted, virus-specific CTL response that peaked 3 days later. Rechallenge of PV-primed mice with homologous virus resulted in a slight but significant increase in spleen NK activity 1 day after reinfection, and this was followed 3 days later by peak CTL activity. Thus, memory cell-mediated immune responses appeared more rapidly after secondary in vivo challenge with PV. Furthermore, the temporal kinetic relationship between virus-induced NK and CTL responses was maintained after both primary and secondary infection with PV, which suggested that virus-induced NK cells may represent pre-CTL.

To investigate the relationship between these two cytotoxic cell populations, expression of lineage specific cell-surface antigens on virus-induced NK and CTL effectors was examined. NK cells induced after primary and secondary infection with PV were found to rapidly acquire the pan-T cell marker Thy-1, which was expressed on mature anti-viral CTL. In addition, asialo-GM 1 (a glycolipid which has been considered a marker of NK cells) appears to be expressed on PV-specific CTLp; treatment of PV-primed spleen cells with a polyclonal rabbit antiserum to this marker plus complement prior to secondary in vitro restimulation with PV-infected macrophages prevented the generation of secondary CTL responses to PV. Furthermore, multiple i.v. injections of this antiserum were able to abrogate the in vivo generation of both NK and CTL responses after primary or secondary infection with PV.

Secondary NK and CTL responses were generated in mice that had been pretreated with cyclophosphamide (CY), suggesting that memory cell-mediated immune responses can be reactivated in vivo without undergoing cell division. In contrast, treatment with CY before primary infection delayed the appearance of virus-induced NK activity and abrogated the generation of H-2 restricted, virus-specific CTL. Rechallenge of these CY-treated, NK-primed mice resulted in the rapid generation of a secondary NK response that was not followed by either a primary or secondary CTL response. This long-term block in CTL generation was not due to the establishment of a persistent PV infection. Memory CTL generation could be restored by secondarily coinfecting mice with PV and a second arenavirus such as Tacaribe virus (TV) or lymphocytic choriomeningitis virus (LCMV), or by injection of interleukin 2 (IL 2)-containing supernatants after rechallenge with PV. To demonstrate that IL 2 was the responsible lymphokine in these supernatants, highly purified IL 2 was added to in vitro cultures of spleen cells from CY-treated, PV-primed mice. In the presence of PV-infected syngeneic macrophages, addition of purified IL 2 resulted in a dose dependent restoration of H-2 restricted, anti-PV CTL activity. In addition, the CTL precursor frequency of CY-treated, PV-primed mice appeared to be markedly reduced compared to that in normal PV-primed mice. Thus, the long-lasting block in the ability to generate PV-specific memory CTL appears to be due to both a lack of helper T cell activity a significant reduction in the number of CTLp. Furthermore, these results suggest that priming the NK compartment is sufficient to prime for a memory CTL response, provided helper factors such as IL 2 are supplied.

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