Immunohistochemical evaluation of the equine endometrium during the oestrous cycle

Effect of ovarian hormones on the healthy equine uterus: a global gene expression analysis

The physiological changes associated with the varying hormonal environment throughout the oestrous cycle are linked to the different functions the uterus needs to fulfil. The aim of the present study was to generate global gene expression profiles for the equine uterus during oestrus and Day 5 of dioestrus. To achieve this, samples were collected from five horses during oestrus (follicle >35 mm in diameter) and dioestrus (5 days after ovulation) and analysed using high-throughput RNA sequencing techniques (RNA-Seq). Differentially expressed genes between the two cycle stages were further investigated using Gene Ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses. The expression of 1577 genes was found to be significantly upregulated during oestrus, whereas 1864 genes were expressed at significantly higher levels in dioestrus. Most genes upregulated during oestrus were associated with the extracellular matrix, signal interaction and transduction, cell communication or immune function, whereas genes expressed at higher levels in early dioestrus were most commonly associated with metabolic or transport functions, correlating well with the physiological functions of the uterus. These results allow for a more complete understanding of the hormonal influence on gene expression in the equine uterus by functional analysis of up- and downregulated genes in oestrus and dioestrus, respectively. In addition, a valuable baseline is provided for further research, including analyses of changes associated with uterine inflammation.

Making sense of equine uterine infections: the many faces of physical clearance

Equine uterine infections inflict major losses on the equine industry. Persistent inflammation of the oviduct and uterus leads to loss of the conceptus and mares susceptible to infection have weakened uterine defences partly due to retention of inflammatory exudate. Bacteria may trigger inflammation, resist phagocytosis, or adhere to the endometrium and types of infection range from genital commensals in susceptible mares to reproductive pathogens in normal mares. Uterine infections are diagnosed by history, detection of uterine inflammation, and isolation of typical organisms and susceptible mares may be identified by detection of intrauterine fluid during oestrus, or at 6-48 h post-breeding. Therapy includes oxytocin, uterine lavage, antibiotics, and prostaglandin analogues and clinical studies indicate additive benefits of oxytocin and antibiotics. Improved conception rates have been associated with autologous, intrauterine plasma, despite controversy about its bactericidal efficacy. Because of the potential for endometrial damage, intrauterine antiseptics require caution.

Uterine clearance and resistance to persistent endometritis in the mare

The objective of this article is to review the role of uterine defense mechanisms in natural resistance to chronic or persistent endometritis. A breakdown of uterine physical clearance mechanisms is currently believed to play a major role in susceptibility to persistent endometritis. Mares with increased susceptibility to persistent endometritis have impaired myometrial contractility in response to an acute inflammation, resulting in an accumulation of fluid and inflammatory products within the uterine lumen. The origin of this defect remains unknown. Recent studies have demonstrated that spermatozoa trigger PMN chemotaxis into the uterine lumen. This observation suggests that a transient endometritis is a normal physiological response to breeding. However, in mares with impaired uterine defense mechanisms, the condition may develop into a persistent endometritis and subsequent subfertility. In contrast to spermatozoa, seminal plasma has a suppressive effect on complement activation and PMN chemotaxis (65). The exact role of seminal components in breeding-induced inflammation needs further investigation.

Immunisation of mares to control endometritis caused by Streptococcus zooepidemicus

Normal mares were immunised by the intramuscular and intrauterine administration of an antigen with adjuvant and they and unimmunised control mares were later challenged by the intrauterine instillation of pathogenic Streptococcus zooepidemicus; the response of all the mares was monitored clinically and bacteriologically for seven days. Significantly fewer S zooepidemicus were present in cervical swabs taken from the immunised mares than from the control mares (P < 0.01) and the degree of inflammation in the genital tract of the immunised mares was also significantly less (P < 0.001). This protective effect of immunisation was associated with the specific IgG response in the serum, and an IgG and IgA response in the uterine secretions. These results are the first demonstration that a previous immunisation with a suitable antigen can reduce an infection of the reproductive tract of mares.

MHC Class II positive cells and T cells in the equine endometrium throughout the oestrous cycle

The quantity and distribution of MHC Class II positive cells and T cells in the equine endometrium was investigated throughout the oestrous cycle. Significantly more MHC Class II positive cells were detected in the stratum compactum and stratum spongiosum of endometria from naturally cycling mares during the follicular than during the luteal phase of the oestrous cycle. Significantly more T cells were also detected in the stratum compactum, but not stratum spongiosum, of these mares during the follicular phase. Furthermore, there was a marked increase in the number of MHC Class II positive cells and T cells in the endometria of ovariectomised mares treated with oestradiol compared with progesterone. An increase in the expression of MHC Class II antigen by endometrial epithelial cells was also observed in mares treated with oestradiol and in some naturally cycling mares during the follicular phase.

Mononuclear cell infiltration of the equine endometrium: immunohistochemical studies

Endometrial sections from mares with varying degrees of mononuclear cell infiltration were examined for immunoglobulin (Ig)A-, IgM-, IgG(T)- and IgG(Fc)-containing cells, luminal and glandular epithelial cell Ig-staining and free interstitial Ig-staining, using a peroxidase anti-peroxidase technique. Mares with mild to moderate (Group 2) and mares with severe diffuse mononuclear cell infiltration, superimposed by acute endometritis (Group 3), had significantly higher numbers of Ig-containing cells than genitally-normal mares (Group 1). The differences between Groups 1 and 3 were significant for all four isotypes. In Groups 1 and 2, numbers of IgA-containing cells were significantly larger than numbers of IgM- and IgG(T)-containing cells. Generally, more glandular epithelial cells stained for IgA and IgM than for IgG(T) and IgG(Fc), and Ig-staining for all isotypes increased from Group 1 to Group 3. Free interstitial staining did not appear to differ among the three groups, but IgG(Fc)- and IgG(T)-staining generally was more intense than IgA- and IgM-staining. The efficiency of uterine defence in the mare does not seem to depend solely on humoral factors, and defects involving other components of the defence system may contribute to failure of the uterus to clear infection.

Plasma cell numbers in uteri of mares with persistent endometritis and in ovariectomised mares treated with ovarian steroids

Immunoglobulins A, G and M were localised by immunoperoxidase staining of endometrial sections from ovariectomised mares. Treatment with progesterone or oestradiol-17 beta did not significantly affect numbers of cells secreting any of the isotypes. Mares with persistent endometritis did not have significantly greater numbers of endometrial plasma cells than genitally-normal mares.