Biomedical Sciences ETDs

Author

Cara Hrusch

Publication Date

7-1-2011

Abstract

Cowpox virus (CPXV), a close relative of variola virus, the orthopoxvirus that causes smallpox, can suppress the immune system through a large array of immunosuppressive gene products. We developed a murine model in which DO11.10 T cells specific for an OVA peptide were transferred into BALB/c mice to assess the impact of a pulmonary CPXV infection on DO11.10 T cell proliferation in lung draining lymph nodes following intranasal OVA peptide delivery. High and low-dose CPXV infections were compared. Both doses lead to clinical illness including ruffled coat and weight loss, but the high dose is lethal and is characterized by viral dissemination to the spleen. A high-dose infection reduced DO11.10 T cell proliferation, but a low-dose infection did not. At the time that proliferation of T cells was assessed (6d post infection), 15±1% of lung dendritic cells (DCs) were infected at the high-dose, but only 5±1% of DCs at the low-dose. At both doses, infected and uninfected lung DCs had decreased expression of MHC class II and the co-stimulatory molecules CD80 and CD86. DCs and T cells were not infected in the lymph nodes at either dose, but lymph node DCs also showed a reduction in antigen-presenting molecules. We speculated that the lung microenvironment created by infection, rather than direct infection of the DCs, suppressed DC antigen-specific T cell activation. In support, we found that alveolar lavage fluid and supernatant derived from lung homogenates from infected mice suppressed the function of uninfected lung DCs in vitro. Furthermore, the suppressive activity was more highly concentrated in lungs from high-dose infected mice. Cytokine analysis revealed the presence of IL-10, an immunosuppressive cytokine, in lung supernatants in mice receiving a high-dose of CPXV. We used IL-10 knockout mice in our adoptive transfer model to examine a role for IL-10 in T cell suppression in the lymph nodes. However, the knockout mice behaved similarly to BALB/c, with lack of DO11.10 T cell proliferation in the high-dose, but not the low-dose, and concluded IL-10 does not prevent T cell proliferation at the high-dose. Finally, we examined a possible virally encoded immunomodulatory protein, a soluble IFNγ receptor (IFNγR), to determine if sequestration of host-produced IFNγ contributed to the immune suppression seen in the high-dose. A mutant virus lacking the IFNγR behaved similarly to wild-type virus, and the survival and day 6 lung titers were comparable. Other virally encoded factors may play a role in suppressing DO11.10 T cell proliferation and should be examined in future experiments. These studies strongly suggest that orthopoxvirus infections create an immunosuppressive microenvironment that compromises the host pulmonary immune responses.

Keywords

Orthopoxvirus, Cowpox virus, Pulmonary Immunity, Lung Infection, Dendritic cell, Murine Model

Sponsors

National Institute of Health, University of New Mexico Infectious Disease and Inflammation Program

Document Type

Dissertation

Language

English

Degree Name

Biomedical Sciences

Level of Degree

Doctoral

Department Name

Biomedical Sciences Graduate Program

First Advisor

Lyons, C. Rick

First Committee Member (Chair)

Lipscomb, Mary

Second Committee Member

Wilder, Julie

Third Committee Member

Ebel, Gregory

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