A differentiation antigen of human large luteal cells in corpora lutea of the menstrual cycle and early pregnancy

To investigate the mechanism(s) of luteal cell differentiation, we raised a monoclonal antibody, HCL-1, against hu man large luteal cells. The antigen was undetectable in growing and preovulatory follicles by immunohistochemistry. The antigen was initially detected on centrally located luteinizing granulosa cells during CL formation. During the midluteal phase, the antigen was expressed at high levels on large luteal cells. Large luteal cells in the CL during late luteal phase and early pregnancy also expressed high levels of HCL-1 antigen, whereas small luteal cells at any stage of the CL did not. Granulosa cells in some atretic follicles weakly expressed HCL-1 antigen. Immunofluorescence staining of enzymatically dispersed luteal cells from human mature CL revealed that HCL-1 antigen was present on the cell surface of large luteal cells. Human granulosa cells isolated from patients who had undergone in vitro fertilization treatment were cultured for 7 days. Indirect immunofluorescence detected HCL-1 antigen on only a few granulosa cells after culture for 1 day and on almost all granulosa cells after culture for 7 days. Flow cytometry of 7-day-cultured cells showed that the percentages of positivity for HCL-1 antigen as well as the mean fluorescence intensities of granulosa cells cultured with hCG (1 IU/ml) were significantly lower than those of the controls (without treatment) (44.3 +/- 3.2% vs. 62.9 +/- 4.0%, p < 0.01; 60.9 +/- 6.7 vs. 82.1 +/- 7.6, p < 0.05). By contrast, the mean fluorescence intensities of cells cultured with interleukin-1 alpha (10 ng/ml, 105 +/- 6.3, p < 0.05) and tumor necrosis factor alpha (10 ng/ml, 112 +/- 11.2, p < 0.05) were significantly higher than those of controls. These findings showed that the cell surface antigen detected on human large luteal cells by HCL-1 was differentiation-related, and that large luteal cells in the CL of pregnancy are derived from granulosa cells via large luteal cells in the CL of the menstrual cycle.