Expression of major histocompatibility complex antigen and timing of invasion by equine chorionic girdle cells cultured on Matrigel

Chorionic girdle cells are a highly invasive subpopulation of trophoblastic cells of the horse conceptus that adhere to the uterine epithelium and begin to invade the endometrium on Days 34-36 (Day 0 = day of ovulation). Just prior to and during invasion (Days 32-36), chorionic girdle cells express high levels of major histocompatibility complex (MHC) I, but expression of this antigen decreases by Days 40-45 and is lost by Day 55. The mechanisms involved in the control of chorionic girdle cell invasion and altered MHCI expression over time are not known. The objective of this study, therefore, was to determine the timing of invasion and the characteristics of MHC expression by girdle cells cultured on Matrigel to determine whether chorionic girdle cell behavior in this environment is similar to the behavior in vivo. Chorionic girdles from four conceptuses were collected on each of Days 30, 31, and 32 and placed in Matrigel invasion chambers for 48 h and in additional duplicate chambers for a time period equivalent to the number of days from the day of collection to Day 36 (6, 5, and 4 days, respectively). After these culture times, the area of the filter covered by invasive cells was determined through use of the software program NIH image. At 48 h, Day 31 and Day 32 girdle cell preparations had invaded Matrigel; but only one Day 30 girdle cell preparation showed invasion into Matrigel, and the extent of invasion was limited. Girdle cells collected on all 3 days had invaded Matrigel by the time equivalent to Day 36. Additionally, chorionic girdles from six conceptuses were collected on Day 34 and placed in Matrigel invasion chambers. Three of these were examined for surface antigen expression bf MHCI, MHCII, and a trophoblast-specific antigen (102.1) by immunocytochemistry (ICC) every 48 h to a time point equivalent to Day 44. The remaining three were examined for these same antigens at times equivalent to Days 36, 40, 50, and 60. Invasive Day 34 girdle cells expressed MHCI and trophoblast-specific antigen, but not MHCII, at each time examined (Days 36-60). Neither the timing of invasion nor MHCI expression by chorionic girdle cells on Matrigel mimicked what occurs in vivo. Therefore, it is likely that the in utero environment plays a role in regulating these two characteristics of equine chorionic girdle cells.