Transmission electron micrographs of C. trachomatis inclusion development in ECC-1 cells at 48 hours under different hormonal conditions estradiol and/or progesterone. (A) ECC-1 cells grown in normal FCS supplemented cell culture. Typical RB forms are present at 24 hours post infection (B) No hormone supplemented stripped FCS media. Once again normal RB morphology was observed under this condition; RBs appeared similar to normal FCS supplemented cell culture. (C) Estradiol supplemented, RBs were distinctly different, appearing as large aberrant form. Estradiol supplementation of infected cells, resulting in smaller inclusions containing enlarged, atypical RB forms (arrows). (D) Progesterone supplemented, shape and morphology of RBs were normal including binary fission. Morphological examination of progesterone exposed cultures with TEM did not show any evidence of aberrant, persistent forms. Magnification: × 20K, marker represent 200 nm.