Depression of humoral responses by murine cytomegalovirus infection

Recurrent cytomegalovirus disease, visceral leishmaniosis, and Legionella pneumonia after liver transplantation: a case report

PURPOSE

Recurrent cytomegalovirus (CMV) disease is a frequent complication of liver transplantation. Visceral leishmaniosis in a transplant recipient is, on the other hand, extremely rare and only two cases of kala-azar have been described after liver transplantation. Immunosuppressed patients are known to be at risk of Legionella infection and the relationship between infection with this organism and hospital water supplies has been well described. These three diseases carry a high mortality rate. Our report examines the potential relationship between these complications.

CLINICAL FEATURES

We describe the case of a liver transplant recipient who presented the three complications successively and survived. After reviewing the literature, we explore hypotheses linking these infections and discuss treatment strategies.

CONCLUSIONS

In the patient described, infection with leishmania probably occurred months prior to the clinical presentation, a delay that matches the incubation period of kala-azar. The simultaneous onset of leishmaniosis and of a high CMV viremia may have been a coincidence. However, CMV infection has been shown to be an independent predictor of invasive fungal infection in liver transplant recipients. CMV does indeed have a suppressive effect on the humoral and cellular immune response in vitro as well as in vivo. The clinical manifestations of leishmaniosis may, therefore, have been precipitated in this patient by the additive immunosuppressive effect of antirejection drugs and CMV.

Characterization of thymic involution induced by murine cytomegalovirus infection

Infection of BALB/c mice with murine cytomegalovirus (MCMV) decreased the numbers of cells recovered from the thymus by 80-90% after 4-7 days, although less than 10 thymocytes per million were productively infected with the virus. A loss of cortical thymocytes was evident in histologic sections and correlated with depletion of CD4+ CD8+ cells. Thymic involution was minimal in C57BL/6 mice. This resistance was not H-2b-associated, as BALB.B (H-2b) mice were severely affected. In CXB recombinant inbred mice, thymic involution and MCMV replication co-segregated with atrophy and infection of the spleen and bone marrow. This suggests common regulation by natural killer (NK)1.1+ cells, consistent with the enhanced thymic involution demonstrated in NK-deficient bg/bg mice. However, CD4- CD8- cells were not depleted, so bone marrow hypoplasia may not be the proximal cause of thymic involution. MCMV infection activated CD4+, CD8+ and CD4+ CD8+ thymocytes, as expression of MEL14, major histocompatibility complex class I (H-2) and Sca-1 antigens increased on these cells. In vitro lymphoproliferation and interleukin (IL)-3 release were enhanced in unseparated and CD4(+)-enriched thymus preparations. Maturation of the thymus population was also evident from the high frequencies of single positive CD4+ and CD8+ cells and the decline in Sca-2 expression. However, unlike peripheral T cells, thymocytes from infected mice did not release IL-2. The results suggest that thymic involution accelerates the transit of cells through the thymus. The possibility that this impairs the elimination of autoreactive T cells within the thymus and promotes the autoimmune manifestations of MCMV disease is discussed.