Pathology of the placenta and cord in ascending and in haematogenous infection.

The two main patterns of inflammatory response in the placenta and its adnexae are: (1) amniotic infection, usually bacterial ascending, with acute chorioamnionitis and funisitis; (2) haematogenous villitis, usually viral, with early necrotizing lesions and vasculitis and, later, chronic infiltrates and obliterative vasculitis. In amniotic infection most cells in the exudate are maternal. These leucocytes participate in antibacterial defence of the amniotic cavity in conjunction with substances such as zinc polypeptide and lysozyme and may contribute directly to fetal defence. Immunoglobulins may be produced in the cord of placenta only in protracted lesions such as 'healed' funisitis. Individual variations in the resistance of the membranes to bacterial penetration are possible. In viral infections a massive multifocal production by plasmacytes of immunoglobulins M, G and A is seen in affected villi. The secretion of non-specific antiviral substances in the infected placenta is possible. In all affected villi there is an activation of fixed macrophages (Hofbauer cells) that remain partly 'immature', i.e. are lysozyme-negative. Multifocal lymphoplasmacytic villitis is uncommon and has helped to focus the diagnosis on prenatal infection. In contrast, non-specific lymphocytic villitis is common; since there is no morphological difference between cases known to be associated with an infection, e.g. varicella, and the others, many cases may well be due to silent infection, although a graft-versus-host reactions remains a distinct possibility.