The effect of intracellular parasitism on cell phenotype

Human peritoneal macrophages were harvested from 'long dwell' peritoneal dialysis bags. Adherent cells were harvested after 2 h culture on plastic and these were then exposed to M. lepraemurium (MLM) or latex beads (LB) for further culture periods of 2 and 24 h. Immunophenotyping of the macrophages was performed before and after culture both with and without the addition of MLM or LB. Monoclonal antibodies RFD1, RFD7 and RFD9 were used, which in control tissues recognize dendritic cells, mature macrophages and epithelioid cells respectively. MoAb RFDR1 (HLA-DR) was also used. Results revealed that the addition of MLM or LD for 2 h did not significantly alter the original proportions of RFD1+ and RFD7+ cells. A proportion of both RFD1+ and RFD7+ cells were found to phagocytose both MLM and LB, although RFD7+ cells seemed slightly more efficient. After 24 h culture with MLM reduced numbers of cells expressed the RFD1+ marker while increased numbers of cells expressing RFD7+ antigen were present. A concurrent small rise in the proportion of RFD7+ cells parasitized implied that this increase was due to RFD1+ cells becoming RFD7+ cells. Culture for 24 h with MLM significantly reduced the percentage of total cells expressing HLA-DR. Conversely, 24 h culture with MLM was shown to increase the proportion of cells expressing the epithelioid cell marker RFD9. These results suggest that intracellular parasitism may affect the expression of surface antigens on cells and by implication thus affect cell function.