Iron deficiency reduces the hydrolysis of cell membrane phosphatidyl inositol-4,5-bisphosphate during splenic lymphocyte activation in C57BL/6 mice

Iron deficiency impairs lymphocyte proliferation in humans and laboratory animals by unknown mechanisms. In this study, we investigated whether this alteration can be attributed in part to impaired hydrolysis of cell membrane phosphatidyl inositol-4,5-bisphosphate (PIP2), a required early event of T-lymphocyte activation. The study involved 46 iron-deficient (ID), 26 control (C) and 23 pair-fed (PF) mice, and ID mice that were repleted for 3 (n = 16), 7 (n = 17) or 14 d (n = 18). Mice were killed after 40-63 d (mean, 48 d) of consuming the test diet (0.09 mmol/kg iron) or the control diet (0.9 mmol/kg). The mean (+/-SEM) hemoglobin concentrations were 57 +/- 16.7, 176 +/- 2.6 and 181 +/- 9.7 g/L for ID, C and PF groups, respectively. After splenic lymphocytes were labeled in vitro with H-3-myoinositol for 3 h, PIP2 hydrolysis was estimated by measuring the radioactivity recovered as a mixture of inositol mono-, di- and triphosphate (IP) from concanavalin A (0, 1, 2.5, 5 and 10 mg/L) activated cells. Although cells from ID mice and those from mice repleted for 3 d incorporated slightly more radioactivity in cellular phospholipids than did cells from C or PF mice, less (P < 0.005) was recovered as IF than in controls, suggesting impaired conversion of the precursor to PIP2. At almost all incubation periods (10-120 min) and mitogen concentrations, the rate of PIP2 hydrolysis expressed as the ratio of radioactivity obtained in Con A-treated to untreated cells was significantly (P < 0.05) reduced in cells from ID mice compared with those obtained from C and PF mice. For cells that were activated for 60 min or less, iron repletion for 14 d significantly (P < 0.05) improved the rate of PIP2 hydrolysis, PIP2 hydrolysis positively and significantly (P < 0.05) correlated (r = 0.27-0.56) with indicators of iron status. Mitogenic response was also significantly (P < 0.05) reduced in ID but not PF mice, and it was corrected by iron repletion for 3, 7 or 14 d. Lymphocyte proliferation positively (r = 0.27-0.37, P < 0.01) correlated with indices of iron status and IP ratios. The data suggest that reduced PIP2 hydrolysis contributes to impaired blastogenesis in iron deficiency.