The concentration of human transferrin (TF) in culture supernatants and intracellular TF contents of normal human peripheral blood mononuclear cells (MNC) after incubation with or without mitogens (PHA, ConA, PWM) for different periods of time were measured by enzyme-linked immunosorbent assay. TF concentrations in culture supernatant tended to gradually increase from the beginning of MNC culture to a peak at day 3 to 5. In contrast, intracellular concentrations of TF were decreased after MNC culture in parallel with the increase of TF concentration in the supernatants. The presence of mitogens mostly diminished TF concentrations in culture supernatant at the time when DNA synthesis maximally occurred. Transferrin release from MNC cultured at 4°C was minimal. A higher iron ion concentration of the culture medium suppressed the TF release from MNC. These results suggested that TF was actually released from MNC when cells were resting but in active metabolism at low iron concentration. In addition, the kinetics of TF release by MNC from systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) patients were different from that of healthy controls. Low spontaneous TF release from SLE MNC through the culture and higher TF release from RA MNC in PHA stimulation after culture for 5 days were observed. These abnormalities found in SLE and RA might be one of causes of the low responsiveness of MNC in these patients to various mitogens.
human peripheral blood mononuclear cells