The results of this study demonstrate that MCP-1 mRNA is present within the bovine CL between Days 15 and 20 of the estrous cycle. Most significantly there is an increased amount of MCP-1 mRNA in CL after functional luteolysis compared to CL in the days leading up to luteolysis. High mRNA expression was seen in one preluteolytic animal in which the PGFM metabolite was elevated at the time of CL collection. Messenger RNA encoding MCP-1 was associated with a number of cell types within the postluteo-lytic CL, including specific populations of CD8+ T lymphocytes. Cheap Diskus Advair
The expression of mRNA encoding MCP-1 in the CL is not unexpected because of the large number of cell types present within luteal tissue that are potential sources of MCP-1. These include endothelial cells, fibroblasts, lymphocytes, and macrophages. These cell types are present throughout the estrous cycle, although their proportions relative to large and small luteal cells vary. Detailed studies will be required to identify all of the different cell types involved in expression of MCP-1 mRNA in the bovine CL.
We have shown previously that there is an increase in the numbers of CD8+ T lymphocytes in bovine luteal tissue from Day 15 of the estrous cycle onward. The role of these cells at this stage of the estrous cycle is not clear, although recently there has been increasing interest in the potential local effects of immune cells and their cytokine products, particularly around key events such as ovulation and luteolysis. Uterine PGF2a is known to be the luteolytic factor in the cow. However, events occurring at the level of the CL around the time of luteolysis are much less clearly defined.
T lymphocytes are a potent source of MCP-1. They may also act indirectly, through their cytokine products, including tumor necrosis factor a and interleukin-1, to promote expression of MCP-1 mRNA by other cell types. In the present study, T lymphocytes were distributed in a pattern similar to that for those cells expressing mRNA for MCP-1 in some areas of luteal tissue. It is possible that one of the roles of the increased numbers of T lymphocytes in the CL around natural luteolysis is the production of MCP-1 to recruit macrophages that are then involved in structural luteolysis. However, it is likely that other, as yet uncharacterized, cell types within the CL are also significant in the production of MCP-1 around the time of luteolysis. Further studies will be required to more clearly identify the cell types involved at different stages of luteolysis.