Binding affinity and quantity of estrogen receptor in peripheral blood monocytes of patients with systemic lupus erythematosus

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Abstract
Binding affinity and quantity of the estrogen receptor in monocytes of patients with sys temic lupus erythematosus (SLE) were studied. The tritiated-estradiol binding assay was performed using peripheral blood adherent cells (>95% monocytes) derived from six lupus patients (SLEDAI score: 2-30) and five age-comparable normal women during the mid- follicular phase of the menstrual cycle. Dissociation constant (Kd) and number of binding sites (Ro) were estimated by Scatchard analysis. The specificity and sensitivity of the assay were verified by using estrogen receptor-positive ZR75-1 human breast cancer cells. Kd and Ro of the type I receptor for the SLE patients were 12.2 ± 6.5 (nM) and 69.0 ± 42.4 ( x 1000/cell), respectively, while those of the normals were 14.5 ± 3.7 and 86.8 ± 23.4, respectively. Three patients displayed relatively low Kd or Ro values. While those low values fell within the mean —3 s.d. of the normal controls, precise statistical comparison was not possible. No clear correlation between the receptor parameters and the SLEDAI scores was noted. Although further studies of a larger number of samples are needed to conclude, these results suggest that peripheral blood monocytes of SLE patients express the estrogen receptor whose Kd and Ro are similar to those of normals.