Functional impairment of PRRSV-specific peripheral CD3+CD8high cells

Area of Science:

• Veterinary Immunology
• Virology
• Cellular Immunology

Background:

• Porcine reproductive and respiratory syndrome virus (PRRSV) replication decreases before neutralizing antibodies appear, suggesting other immune mechanisms are involved.
• Alveolar macrophages are key targets for PRRSV, and their elimination by immune cells is crucial for viral clearance.

Purpose of the Study:

• To investigate the role of PRRSV Lelystad virus (LV)-specific cytotoxic T-lymphocytes (CTL) in eliminating PRRSV-infected alveolar macrophages.
• To assess the CTL response in pigs experimentally infected with PRRSV.

Main Methods:

• Cytotoxic T-lymphocyte (CTL) assays were performed using PRRSV-infected alveolar macrophages as target cells.
• Autologous peripheral blood mononuclear cells (PBMC) from PRRSV-infected pigs were used as a source of PRRSV-specific CTL.
• Assays were validated using pseudorabies virus (PRV) Begonia-infected cells and PBMC.

Main Results:

• No detectable CTL activity against PRRSV-infected macrophages was observed in freshly isolated PBMC from PRRSV-infected pigs up to 56 days post-infection (dpi).
• Restimulation of PBMC with PRRSV in vitro induced proliferation of CD3+CD8high cells from 14 dpi, but significant CTL activity was delayed until 49-56 dpi in only one pig.
• In contrast, PRV-specific CTL activity was observed robustly from 21 dpi in control pigs.

Conclusions:

• PBMC from PRRSV-infected pigs contain CD3+CD8high cells that proliferate upon in vitro restimulation.
• These PBMC, however, fail to effectively eliminate PRRSV-infected alveolar macrophages, indicating a lack of functional PRRSV-specific CTL response during the study period.