Lymphoid tissue could be a latent tissue reservoir in XMRV infection

Marta Curriu1, J Carrillo1, M Massanella1, E Garcia1, B Clotet1, C Carrato2, J Blanco1, and C Cabrera1:

XMRV Induces a Nonproductive Infection in Human Lymphoid Tissue
1Fndn irsiCaixa, Badalona, Spain and 2Hosp Univ Germans Trias i Pujol, Barcelona, Spain
Background: Xenotropic murine leukemia virus-related virus (XMRV) has been associated with prostate cancer and chronic fatigue syndrome. In humans the virus has been found in a variety of cell types, including T and B cells, and in rhesus macaques there is evidence for viral replication in lymphoid organs, suggesting that lymphocytes are a target for XMRV. Histocultures of tonsils support productive infection with various viruses, including HIV and human herpesvirus 6. In this study, ex vivo lymphoid tissue was used to investigate the pathogenic mechanisms of XMRV.

Methods: Tonsils from 2 healthy individuals undergoing tonsillectomy were collected and cultured in small pieces (2 mm3) over gelfoam soaked in RPMI medium. Tissue blocks were left uninfected or infected with XMRV stock obtained from a 22Rv1 cell supernatant. Culture medium was replaced every 3 days. After 14 days in culture, both tissues were homogenized and cells were isolated. Viral infection was evaluated at different times in the cells migrating out the tissue and at day 14 in tissue cells by PCR, analyzing viral DNA. In addition, tissue cells were immunophenotyped by flow cytometry and the presence of envelope protein (env) was analyzed by Western blot (WB) using an antibody to SFFV env that reacts with all poly- and xenotropic murine leukemia virus.

Results: Seven days post-infection cells migrating out the tissue were positive for XMRV DNA. After 14 days of culture, tissue cells were also positive, confirming that XMRV infected human tonsil tissue in the absence of exogenous stimulation. Despite the presence of XMRV DNA, infection does not seem to be productive since tissue lysates exhibited undetectable expression of XMRV env proteins by WB. Uninfected and infected tissues showed similar percentages of T and B cells. XMRV infection did not modify the percentage of CD3 (76 and 75% in XMRV+ and XMRV– tissue, respectively), CD4 (53% vs 52%), CD8 (39% vs 40%), or CD19 cells (3% vs 1%). A deeper analysis of T cell subsets showed that XMRV infection did not modify the naïve/memory cell ratio, or immune activation markers, as evaluated by the expression of HLA-DR and CD38.

Conclusions: Our data show that XMRV could be integrated into the human lymphoid tissue cells although this process does not culminate in an explicit productive infection. In addition, this infection did not result in changes of T or B cells nor an immune activation, suggesting that lymphoid tissue could be a latent tissue reservoir in XMRV infection.