Presence of Subepithelial Lymphoid Nodules in the Teat of Ewes

Investigating mammary glands of lactating goats for the presence of tertiary lymphoid organs

Ectopic tertiary lymphoid organs (TLOs) have been identified in many organs, such as the lungs, nasal cavities, and kidneys of both mice and humans. Although lymphocyte aggregates have been observed in the mammary glands of ruminants, the details remain unclear. In this study, we investigated the mammary glands of lactating goats for the presence of TLOs. The localization of CD20 (B cells), CD3 (T cells), MECA79 (high endothelial venules), CD40 (follicular dendritic cells), BCL6 (germinal center), and IgA was examined by immunohistochemistry. The concentrations of IgG, IgA, lactoferrin, β-defensin-1, cathelicidin-2, cathelicidin-7, S100A7, and S100A8 in milk were measured by ELISA. The localization and amount of tight junction (TJ) proteins (claudin-3 and claudin-4) were examined using immunofluorescence and western blotting. We found that 19 out of 30 udders contained lymphocyte aggregates, which showed positive reactions against CD20, CD3, CD40, and MECA79. In addition, large-sized aggregations showed separate localization of B cells and T cells and a positive reaction against BCL6, although BCL6 was sparsely localized in the aggregations. These results indicate that mammary glands of lactating goats contain TLOs. The IgG and IgA concentrations in the milk of TLO-positive goats and the number of IgA-positive cells were higher than those in negative goats. Furthermore, claudin-4 was localized in the TJ region and the amount was higher in TLO-positive mammary glands than that in the negative group, indicating the presence of leakages at TJs. In conclusion, a majority of lactating goat udders have TLOs, which contribute to local immunity by producing immunoglobulins.

Adaptive Cell-Mediated Immunity in the Mammary Gland of Dairy Ruminants

Mastitis is one of the greatest issues for the global dairy industry and controlling these infections by vaccination is a long-sought ambition that has remained unfulfilled so far. In fact, gaps in knowledge of cell-mediated immunity in the mammary gland (MG) have hampered progress in the rational design of immunization strategies targeting this organ, as current mastitis vaccines are unable to elicit a strong protective immunity. The objectives of this article are, from a comprehensive and critical review of available literature, to identify what characterizes adaptive immunity in the MG of ruminants, and to derive from this analysis research directions for the design of an optimal vaccination strategy. A peculiarity of the MG of ruminants is that it does not belong to the common mucosal immune system that links the gut immune system to the MG of rodents, swine or humans. Indeed, the MG of ruminants is not seeded by lymphocytes educated in mucosal epithelia of the digestive or respiratory tracts, because the mammary tissue does not express the vascular addressins and chemokines that would allow the homing of memory T cells. However, it is possible to elicit an adaptive immune response in the MG of ruminants by local immunization because the mammary tissue is provided with antigen-presenting cells and is linked to systemic mechanisms. The optimal immune response is obtained by luminal exposure to antigens in a non-lactating MG. The mammary gland can be sensitized to antigens so that a local recall elicits neutrophilic inflammation and enhanced defenses locally, resulting from the activation of resident memory lymphocytes producing IFN-γ and/or IL-17 in the mammary tissue. The rational exploitation of this immunity by vaccination will need a better understanding of MG cell-mediated immunity. The phenotypic and functional characterization of mammary antigen-presenting cells and memory T cells are amongst research priorities. Based on current knowledge, rekindling research on the immune cells that populate the healthy, infected, or immunized MG appears to be a most promising approach to designing efficacious mastitis vaccines.

Size of supernumerary teats in sheep correlates with complexity of the anatomy and microenvironment

Supernumerary nipples or teats (polythelia) are congenital accessory structures that may develop at any location along the milk line and have been implicated in the pathogenesis of mastitis. We describe the anatomy and histology of 27 spontaneously occurring supernumerary teats from 16 sheep, delineating two groups of teats - simple and anatomically complex - according to the complexity of the anatomy and microenvironment. Anatomically complex supernumerary teats exhibited significantly increased length and barrel diameter compared with simple supernumerary teats. A teat canal and/or teat cistern was present in anatomically complex teats, with smooth muscle fibres forming a variably well-organised encircling teat sphincter. Complex supernumerary teats also exhibited immune cell infiltrates similar to those of normal teats, including lymphoid follicle-like structures at the folds of the teat cistern-teat canal junction, and macrophages that infiltrated the peri-cisternal glandular tissue. One complex supernumerary teat exhibited teat end hyperkeratosis. These anatomical and histological features allow inference that supernumerary teats may be susceptible to bacterial ingress through the teat canal and we hypothesise that this may be more likely in those teats with less well-organised encircling smooth muscle. The teat cistern of anatomically complex teats may also constitute a focus of milk accumulation and thus a possible nidus for bacterial infection, potentially predisposing to mastitis. We suggest that size of the supernumerary teat, and relationship to the main teats, particularly in the case of 'cluster teats', should be considerations if surgical removal is contemplated.

Characterization of minimal lesions related to the presence of visna/maedi virus in the mammary gland and milk of dairy sheep

Background

In order to characterize the complete range of lesions, especially minimal, affecting mammary gland and viral antigen distribution and target cells using immunohistochemistry in naturally Visna/maedi (VM) 84 infected sheep were studied, forty-four from flocks with clinical cases (A) and 35 randomly sampled from two abattoirs (B) together with five negative controls (C). An immunocytochemistry technique was developed and further milk samples (n = 39) were used to study viral excretion, carrier cells and the role of milk and colostrum in the transmission of the disease.

Results

All sheep from group C and three sheep from group B were negative to VM in tissue sections by histopathology, immunohistochemistry and PCR, and also in serum using ELISA. Several degrees of CD3 + lymphocytic interstitial mastitis were observed in groups A and B: minimal (+) n = 26 sheep; moderate (++), n = 32 and severe (+++), n = 12. No differences in lesion distribution were observed between groups A and B. Viral presence was confirmed by immunohistochemistry using two different antibodies and/or PCR in every tissue with lesions while serology was negative in six sheep with lesions. Two milk samples taken from milk tanks from two flocks from group A and fourteen milk samples from 29 infected sheep from group B were positive to VM (most of them from animals with moderate and severe lesions). Positivity was only found in macrophages, even in focal and minimal lesions, while no positivity was observed in epithelial or any other cells in either tissue and milk samples.

Conclusions

This new observation of the minimal lesions described in this work increased the prevalence of VM lesions in mammary gland up to 90.9% and VM should be considered as a differential diagnosis when minimal interstitial lesions are detected. A high prevalence of VM was observed in intensive milk-producing sheep, ELISA serology did not detect as positivity all infected animals, while histology, IHC or PCR showed higher sensitivity. The cytological technique developed was very useful in milk-cell studies using hematoxylin and eosin and immunocytochemistry. Viral detection in milk samples (16/39) confirms a potential but limited role of milk/colostrum in viral transmission.

Electronic supplementary material

The online version of this article (10.1186/s12917-019-1855-3) contains supplementary material, which is available to authorized users.

The Mammary Microenvironment in Mastitis in Humans, Dairy Ruminants, Rabbits and Rodents: A One Health Focus

The One Health concept promotes integrated evaluation of human, animal, and environmental health questions to expedite advances benefiting all species. A recognition of the multi-species impact of mastitis as a painful condition with welfare implications leads us to suggest that mastitis is an ideal target for a One Health approach. In this review, we will evaluate the role of the mammary microenvironment in mastitis in humans, ruminants and rabbits, where appropriate also drawing on studies utilising laboratory animal models. We will examine subclinical mastitis, clinical lactational mastitis, and involution-associated, or dry period, mastitis, highlighting important anatomical and immunological species differences. We will synthesise knowledge gained across different species, comparing and contrasting disease presentation. Subclinical mastitis (SCM) is characterised by elevated Na/K ratio, and increased milk IL-8 concentrations. SCM affecting the breastfeeding mother may result in modulation of infant mucosal immune system development, whilst in ruminants notable milk production losses may ensue. In the case of clinical lactational mastitis, we will focus on mastitis caused by Staphylococcus aureus and Escherichia coli. Understanding of the pathogenesis of involution-associated mastitis requires characterization of the structural and molecular changes occurring during involution and we will review these changes across species. We speculate that milk accumulation may act as a nidus for infection, and that the involution 'wound healing phenotype' may render the tissue susceptible to bacterial infection. We will discuss the impact of concurrent pregnancy and a 'parallel pregnancy and involution signature' during bovine mammary involution.

Sinus-like dilatations of the mammary milk ducts, Ki67 expression, and CD3-positive T lymphocyte infiltration, in the mammary gland of wild European rabbits during pregnancy and lactation

Sinus-like dilatations of the mammary duct are recognisable in the mammary gland of pregnant and lactating wild European rabbits. These dilatations exhibit a bilaminar epithelial lining, with luminal epithelial cells expressing basal and lateral E-cadherin. Occasional binucleated mammary epithelial cells are present in the luminal layer. Underlying the luminal epithelial cells is a basal layer of cytokeratin 14-positive cells, supported by a thin layer of fibrous tissue. Multi-segmental epithelial proliferation, as indicated by Ki67 expression, is apparent in the luminal epithelial cells, suggesting a capacity for division during pregnancy and lactation. CD3-positive T lymphocytes are present both intraepithelially, suggesting exocytosis, and in foci subjacent to the ductular epithelium. We consider that sinus-like dilatations of the mammary duct may have the potential to give rise to a subset of the mammary gland neoplasms classified as ductal in origin. Milk accumulation in these sinus-like dilatations is likely to provide a niche for bacterial replication in cases of mastitis in rabbits. These structures are an important component of the innate immune system of the mammary gland, both as a physical barrier and as an interface between the milk and mammary immune cells.

PERSISTÊNCIA DE STAPHYLOCOCCUS COAGULASE-NEGATIVOS EM GLÂNDULAS MAMÁRIAS DE OVELHAS COM MASTITE SUBCLÍNICA APÓS O TRATAMENTO ANTIMICROBIANO À SECAGEM

Resumo Staphylococcus coagulase-negativos (SCN) são os principais micro-organismos responsáveis pela mastite ovina e o tratamento ao final da lactação pode ser usado como método de controle contra a doença. Porém, o longo período seco apresentado pelas ovelhas em alguns sistemas de criação pode prejudicar os efeitos positivos do tratamento antimicrobiano. Os objetivos deste trabalho foram identificar as principais espécies de SCN na etiologia da mastite ovina antes e após o tratamento ao final da lactação das ovelhas, bem como investigar a persistência das espécies mais prevalentes na glândula mamária na lactação seguinte. Sessenta ovelhas foram divididas em dois grupos experimentais, um deles formado por animais sem tratamento antimicrobiano, enquanto o outro era composto por ovelhas cujas metades mamárias foram tratadas com cloxacilina-benzatina por via intramamária. As amostras de leite foram obtidas antes da secagem e aos 15 e 30 dias após o parto da lactação seguinte. As espécies prevalentes foram S. warneri, S. simulans e S. epidermidis. Clones das três espécies de maior ocorrência foram identificados antes e depois do tratamento, ou seja, mesmo com o extenso período seco entre as duas lactações consecutivas, os micro-organismos ainda foram identificados no interior da glândula mamária.

Transmission of Mannheimia haemolytica from the tonsils of lambs to the teat of ewes during sucking

Objective of the work was to study whether Mannheimia haemolytica may be transmitted from the mouth of the lambs into the teat of the dam during sucking. We compared bacterial populations within the teat duct and milk of ewes immediately before and immediately after sucking by the lambs. Tonsils of lambs of the ewes were swabbed. M. haemolytica strain DAG21T recovered from a teat duct of a ewe was compared to strain DAG21R recovered from the tonsils of her lamb by using 16s rRNA sequencing. We used those two isolates and another one of known pathogenicity, for challenging ewes: (i) 2 mm deep into healthy teats, (ii) 2 mm deep into teats with chapping lesions or (iii) into the cistern of healthy mammary glands. Of samples collected before suckling, 20/792 were bacteriologically positive, and of those after, 50/792 were bacteriologically positive (P<0.001); in 37 cases, a negative sample became positive. One M. haemolytica (DAG21T) was recovered after suckling from a teat duct of a ewe. The organism was isolated from 57/90 tonsillar swabs from lambs. Risk of infection of ewe' teats was 0.004 throughout lactation, being greatest (0.021) during the 3rd week of lactation. The 16s rRNA sequences of strains DAG21T and DAG21R were identical over 1450 nucleotides. Phylogenetic analysis showed that the two isolates clustered together with isolates of M. haemolytica. Organism deposition into healthy teats caused subclinical mastitis; deposition into teats with lesions or directly into mammary gland caused clinical mastitis. When results of inoculation of the three strains were compared between them, statistical significance was always P>0.9. Results provide clear evidence that suckling by lambs can lead to transmission of M. haemolytica into the teats of the ewes; the bacteria have the potential to cause mastitis if circumstances are favourable.

The bacterial flora in the teat duct of ewes can protect against and can cause mastitis

We studied the possible effects of bacterial populations within the teat duct, in the pathogenesis of ovine mastitis. In experiment I, 32 ewes were allocated into group A (ewes from which we isolated (+++ growth) coagulase-negative staphylococci), B (ewes from whose duct we isolated (+ growth) coagulase-negative staphylococci) or C (ewes from which we isolated Bacillus spp.) and subdivided into A1, B1, C1 (n=4; challenged by deposition of 1.250 cfu of Mannheimia haemolytica into the teat duct) or A2, B2, C2 (n=4; used as uninoculated controls); group D (n=8) contained ewes with no bacteria in their teat ducts and were challenged as above. There were less bacteriological isolations of flora (P = 0.018) and challenge (P<0.05) organisms from A1 than from A2 and D ewes; the severity of pathological findings in A1 (summed up score: 27) ewes was smaller than in D (summed up score: 36) ewes (P = 0.038). No such findings were evident with B1 or C1 ewes (P>0.4). In experiment II, ewes (groups E and F, n=6) from whose duct we isolated coagulase-negative staphylococci (+ growth) were used; in group G (n=6) ewes with no bacteria in their teat ducts were included. Teat chapping was applied in E and G ewes. All E ewes developed acute clinical mastitis within 24 h after teat chapping, although we had carried out no challenge; there were more bacteriological isolations of flora organisms from E than from F and G ewes (P < 0.001); the severity of pathological findings in E (score: 28) was greater than in F (score: 3) or G (score: 14) ewes. In experiment III, eight ewes with no bacteria in their teat ducts were allocated into group H or I (n=4) and challenged into the teat (group H) or into the gland (group I) with 10(6) cfu of a Staphylococcus simulans recovered from the teat duct of a group E ewe. Group H ewes developed transiently clinical followed by subclinical mastitis (based on bacteriological and cytological evidence), whilst group I ewes developed severe clinical disease. We conclude that staphylococcal flora present in high numbers within the teat duct of ewes can afford some protection against invading microorganisms. However with impeded defence mechanisms of the teat, the same flora may invade the mammary parenchyma and cause clinical mastitis.