Mycoplasma infection of rat basophilic leukemia cells and establishment of rat mast cell lines

Results from this study show that a previously identified receptor for IgE with a M{dollar}sb{lcub}rm r{rcub}{dollar} of about 71kDa(71K) is induced by the action of Mycoplasma hyorhinis infection of rat basophilic leukemia (RBL) cells. This induction is reversible; decontamination either in vitro or in vivo leads to a disappearance of 71K and re-infection causes its reappearance. The expression of 71K, appearing within 24h post-infection, is induced as a result of oxidative structural alteration of the {dollar}alpha{dollar} chain of Fc{dollar}varepsilon{dollar}RI on the cell surface. Thus, under reducing condition, 71K is resolved into two components, Fc{dollar}varepsilon{dollar}RI({dollar}alpha{dollar}) and a faintly surface {dollar}sp{lcub}125{rcub}{dollar}I-labelled component. Other effects of infection include reduction in the expression of transferrin receptors and increased histamine content of infected cells. In the presence of cell-bound IgE, mycoplasma induction of 71K on RBL cells is inhibited. However, cell-bound IgE is degraded into fragments of 186kDa, 158kDa and 115kDa, all of which remain receptor-bound. Upon reduction, these degradation products yield 67kDa and 55kDa {dollar}varepsilon{dollar} chain-derived fragments with a loss of L chains indicating that the degradation involves the N-terminus of cell-bound IgE. In the absence of mycoplasma infection, the cell-bound IgE remains relatively intact with a M{dollar}sb{lcub}rm r{rcub}{dollar} of 210kDa.; In a separate study, continuously proliferative cell lines (RCMC) have been established by extended culture of purified rat peritoneal mast cells, typical of the connective tissue-type (CTMC), without the requirement of exogenous growth factors such as IL-3 and IL-4, or accessory cells. Although the RCMC lines were derived from CTMC, they exhibit phenotypic characteristics of mucosal-type mast cells (MMC), i.e., they contain the enzyme marker for MMC (RMCPII), relatively low histamine content and stain alcian blue{dollar}sp+{dollar}/safranin{dollar}sp-{dollar}. The established cell lines, RCMC1 to 9, exhibit variable levels of receptor expression of Fc{dollar}varepsilon{dollar}RI and Fc{dollar}varepsilon{dollar}RII. In addition, at the early stages of cell culture, RCMC1 expressed predominantly Fc{dollar}varepsilon{dollar}RI and an increase in the expression of Fc{dollar}varepsilon{dollar}RII has been observed with time in culture. Characterization of clones of RCMC1 indicates that the appearance of Fc{dollar}varepsilon{dollar}RII may be attributable to an outgrowth of clones with predominant expression of Fc{dollar}varepsilon{dollar}RII as well as an expression of Fc{dollar}varepsilon{dollar}RII on cells originally devoid of this receptor.