Immune cells and cytokine production in the bovine corpus luteum throughout the oestrous cycle and after induced luteolysis

Immune cells and their cytokine products have powerful local effects within body tissues. There has been great interest in the potential role of these cells, not only during destruction of the corpus luteum but also during it s functional lifespan. Ln this study, lymphocytes, macrophages and major hi stocompatibility complex class II molecules were quantified using immunohis tochemistry and the reverse transcription-polymerase chain reaction was use d to detect mRNA for tumour necrosis factor alpha and interferon gamma with in corpora lutea from three groups of cows: (1) corpora lutea collected at an abattoir and assessed visually into four stages (stage I (days 1-5), sta ge II (days 6-12), stage III (days 13-18) and stage IV (days 19-21) of the oestrous cycle); (2) corpora lutea collected around natural luteolysis (day s 14-20); and (3) corpora lutea collected 6, 12 and 24 h after prostaglandi n F-2 alpha-induced luteolysis. The numbers of T lymphocytes (CD5+ and CD8( +)) were significantly higher (P < 0.05) at stage IV and from day 16 onward s, before functional luteolysis. There were significantly higher numbers (P < 0.01) of macrophages at stages I, III and IV compared with stage IT in v isually staged tissue. Major histocompatibility complex class II molecules were increased (P < 0.05) at stages I and IV compared to stage II and at al l times after induced luteolysis. Using reverse transcription-polymerase ch ain reaction, mRNA encoding tumour necrosis factor a and interferon gamma w as detected in all luteal tissue collected around natural luteolysis and af ter induced luteolysis. These findings, particularly the increase in T lymp hocytes before functional luteolysis, provide further evidence of a signifi cant role for the immune system in affecting reproductive function in cows.