Characterization of the fetal inflammatory response to cytomegalovirus placentitis. An immunohistochemical study.

The histopathologic features of cytomegalovirus placentitis, an established cause of chronic villitis, are well documented. However, the immunologic features of the fetal inflammatory response to placental cytomegalovirus infection are largely unknown. The characterization of the fetal-derived inflammatory cell reaction may be important in our understanding of both the intrauterine as well as the antenatal immunological response of the neonate to this important viral infection. We examined formalin-fixed placentas from four cases of confirmed congenital cytomegalovirus infection using an in situ DNA probe to cytomegalovirus, and a variety of antibodies to leukocyte antigens, including anti-CD68, CD45RO, CDw75, CD74, IgG, IgM, and IgA. All four placentas showed marked hyperplasia of fetal-derived placental macrophages, termed Hofbauer cells. A lymphocytic villitis was present in all placentas, which was characterized by positive staining in all cases with T-cell antibodies. There was no evidence of positive staining of lymphocytes using B-cell antibodies in any of the cases. Two placentas showed plasmacellular villitis, which stained positively for both IgG- and IgM-secreting cells, that was present as early as the second trimester of gestation. No IgA positivity of plasma cells was observed. These data are presented in light of current theories of fetal viral immunity.