The Fc receptor for IgA expression and affinity on lymphocytes and macrophages.

The interaction between the Fc receptor for IgA (FcR alpha) and human secretory IgA (sIgA) was studied in a heterologous system by using rabbit alveolar macrophages or splenic lymphocytes. The capacity of FcR alpha-bearing cells to interact with the ligand via the Fc region was demonstrated. The proportion of FcR alpha-bearing lymphocytes and macrophages was found to be 11 and 17%, respectively. The cell-bound radiolabelled ligand showed a release half-time of 70 min for lymphocytes and 45 min for macrophages. The equilibrium constant (K) and the maximum number of ligand molecules bound per cell (n) in mean values was 5.2 +/- 0.05 X 10(8) M-1 and 3.3 +/- 0.15 X 10(5) molecules per cell, respectively. Increased percentages of FcR alpha-bearing cells and of ligand density per cell were obtained after stimulation by lung inflammation. A significant increase of the K value was recorded with macrophages from rabbits with lung acute inflammation (mean value 7.3 +/- 0.21 + 10(8) M-1) while the increase with lymphocytes was not significant. The calculation method of K and n is discussed.