Interstitial pneumonitis during murine cytomegalovirus infection and graft-versus-host reaction: Characterization of bronchoalveolar lavage cells

Acute murine cytomegalovirus (MCMV) infection alters the course of graft-vs-host (GVH) disease involving major histocompatibility (MHC) antigens and induces interstitial pneumonitis. F₁ (B10xB10.BR) mice given 20x10⁶ B10.BR spleen cells and MCMV (1x10⁵ plaque-forming units [PFU]) develop severe, diffuse pneumonitis not seen with either MCMV or GVH alone. As one index of the host immune processes operating in the lungs during MCMV/GVH pneumonitis, we examined the types of cells recovered from the lung by bronchoalveolar lavage (BAL) during pneumonitis. During MCMV/GVH pneumonitis, the total cells recovered significantly increased, due primarily to an influx of Thy 1.2 lymphocytes. Characterization of cells using multiparameter flow cytometric analysis revealed that >80% of all BAL cells were Thy 1.2-positive lymphocytes of donor origin. In addition, donor Thy 1.2-positive cells were of both the L3T4⁺ (43% of BAL cells) and Lyt 2⁺ (38% of BAL cells) phenotype. Thus, MCMV infection during GVH to MHC antigens induces interstitial pneumonitis, characterized by an influx of T lymphocytes (both helper and suppressor/cytotoxic) from the donor. The antigenic specificity of these cells is not known.