Guinea pig cytomegalovirus GP129/131/133, homologues of human cytomegalovirus UL128/130/131A, are necessary for infection of monocytes and macrophages.

The GP129, GP131 and GP133 genes of guinea pig cytomegalovirus (GPCMV) are homologues of human cytomegalovirus UL128, UL130 and UL131A, respectively, which are essential for infection of endothelial and epithelial cells, and for viral transmission to leukocytes. Our previous study demonstrated that a GPCMV strain lacking the 1.6 kb locus that contains the GP129, GP131 and GP133 genes had a growth defect in animals. Here, we demonstrated that the WT strain, but not the 1.6 kb-deleted strain, formed capsids in macrophages prepared from the peritoneal fluid. To understand the mechanism, we prepared GPCMV strains defective in each of GP129, GP131 and GP133, and found that they were all essential for the infection of peritoneal, splenic and PBMC-derived macrophages/monocytes, and for expression of immediate-early antigens in the macrophages/monocytes, although they were dispensable for infection of fibroblasts. Monocyte/macrophage tropism could be one of the important determinants for viral dissemination in vivo.