The impact of CMV on the respiratory burst of macrophages in response to Pneumocystis carinii

Abstract

Infection of human monocyte-derived macrophages with CMV decreased the respiratory burst when cells were stimulated with opsonized zymosan or Pneumocystis carinii (P. carinii). Such an effect, though smaller, was also seen with heat-inactivated CMV, but only when triggered by zymosan. The effect was most pronounced in cells obtained from CMV antibody-negative donors. Dexamethasone further reduced the respiratory burst, both in uninfected and CMV-infected cells. Interferon-gamma increased the response in uninfected cells and, to a lesser extend, in cells treated with heat-inactivated CMV, whereas no effect was seen with infective CMV. No overt productive infection or cytopathology could be detected, however, the monocytes incubated with infective but also heat-inactivated CMV formed clusters, a phenomenon that was equally pronounced in cultures from CMV antibody positive and negative-donors. These results might help explain the worse prognosis of P. carinii pneumonia in patients coinfected with CMV and receiving dexamethasone.

Fig. 1

Effect of CMV on Zymosan-induced respiratory burst of mononuclear cells. The cells were seeded and after 24 h infected with CMV at a multiplicity of infection of 0·5 or treated with an equivalent amount of inactivated virus or with pure medium. After 7 days of culture, the cells were assayed for zymosan-induced chemiluminescence. (a) represents the results from all examined donors (n = 12); (b) the stratified results from CMV seronegative (n = 7) and (c) the stratified results from CMV seropositive (n = 5) donors. All examinations were performed with triplicate cultures. Columns represent the mean results from the indicated experiments, and bars indicate the S.E.M. of the means from each experiment.

Fig. 2

Effect of CMV on P. carinii-induced respiratory burst of mononuclear cells. Twenty-four h after seeding the cells were infected with CMV at a multiplicity of infection of 0·5 or were treated with an equivalent amount of inactivated virus or pure medium. After 7 days of infection, the cells were assayed for chemiluminescence response to opsonized P. carinii. (a) represents the results from all examined donors (n = 14); (b) the stratified results from CMV seronegative (n = 6) and (c) the stratified results from CMV seropositive (n = 8) donors. All examinations were performed with triplicate cultures. Columns represent the mean results from the indicated experiments, and bars indicate the S.E.M. of the means from each experiment.

Fig. 3

Effect of dexamethasone and IFN-γ on the P. carinii-induced respiratory burst of CMV-infected and uninfected mononuclear cells. Cells were treated with dexamethasone (1 µm) during all 8 days of culture or treated with IFN-γ (100 IU/ml) for the last 48 h of culture. Furthermore, cells were either left uninfected (a), were infected with CMV at a multiplicity of infection of 0·5 (c), or were treated with an equivalent amount of inactivated virus as indicated (b). After 7 days of infection the cells were assayed for chemiluminescence response to opsonized P. carinii. All experiments were performed with triplicate cultures. Columns represent the mean results from 7 experiments, and bars indicate the S.E.M. of the means from each experiment.

Fig. 4

Infectious CMV in cultures of mononuclear cells. Cells were seeded and after 24 h infected with CMV at a multiplicity of infection of 0.5. (▪). After 1 h of adsorption the virus-containing medium was removed, and fresh culture medium was added (indicated by the arrow). At the indicated time after infection, cultures were assayed for extracellular (•) and cell-associated (○) infectious CMV. Each point represents the titre of CMV in one culture, and the lines are drawn between the mean log-titre in each group.

Fig. 5

Morphology of CMV-infected and uninfected mononuclear cells. Cells were seeded and after 24 h infected with CMV at a multiplicity of infection of 0·5 (a), or treated with an equivalent amount of heat-inactivated virus (b) or with pure medium (c). After 6 days of infection micrographs were taken. The bar indicates 100 µ m.