In vitro models for host-parasite interactions involving mycoplasmas

Model systems for the study of mycoplasma infections are available with various degrees of complexity. They offer the advantages of simplicity and control of environmental variables. More significantly, they have a homogeneity of cell type, which is necessary when analyzing the biochemical factors in pathogenicity. Cell cultures of fibroblasts are especially useful in studies of receptor sites. Human lung fibroblasts in monolayer format contain a sialoglycoprotein to which Mycoplasma pneumoniae attaches. Fibroblast membranes are extracted with lithium diiodosalicylate or Triton X-100 to provide a fraction rich in glycoprotein. Polyacrylamide gel electrophoresis revealed less than eight proteins, with the majority of the carbohydrate in a single zone. Autoradiography of gels from fibroblasts grown in radiolabeled medium revealed that this zone also had high concentrations of glucosamine. Detergent extracts competitively inhibited the attachment of M. pneumoniae to fibroblasts. Cultures of fibroblasts also have been used to show that M. pneumoniae disrupts de novo purine synthesis within hours after infection. Monolayers of ciliated respiratory epithelial cells displayed an even distribution of receptor sites over the cell membrane. Intact trachea perfusion cultures were used to establish the pattern of pathogen distribution in upper airways. These in vitro approaches provide valuable insight into the process of mycoplasma attachment and the subsequent metabolic alterations that cause cytotoxicity.