Effects on adhesion molecule expression and lymphocytes in the bovine mammary gland following intra-mammary immunisation

Immune defences of the mammary gland in dairy ruminants

The mammary gland (MG) of ruminants is essential for assuring the immune protection and nutrition of the suckling youngs. The domestication of these species aimed at increasing milk production for human consumption enhanced udder susceptibility to infections and in this context, a better understanding of the MG immune defences has become a cornerstone for the success of dairy farming. In this review, we explore constitutive and inducible immune mechanisms of the mammary gland and briefly discuss the knowledge gaps that remain to be elucidated for the implementation of strategies focused on boosting mammary immune responses.

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.

Progress towards the Elusive Mastitis Vaccines

Mastitis is a major problem in dairy farming. Vaccine prevention of mammary bacterial infections is of particular interest in helping to deal with this issue, all the more so as antibacterial drug inputs in dairy farms must be reduced. Unfortunately, the effectiveness of current vaccines is not satisfactory. In this review, we examine the possible reasons for the current shortcomings of mastitis vaccines. Some reasons stem from the peculiarities of the mammary gland immunobiology, others from the pathogens adapted to the mammary gland niche. Infection does not induce sterilizing protection, and recurrence is common. Efficacious vaccines will have to elicit immune mechanisms different from and more effective than those induced by infection. We propose focusing our research on a few points pertaining to either the current immune knowledge or vaccinology approaches to get out of the current deadlock. A possible solution is to focus on the contribution of cell-mediated immunity to udder protection based on the interactions of T cells with the mammary epithelium. On the vaccinology side, studies on the orientation of the immune response by adjuvants, the route of vaccine administration and the delivery systems are among the keys to success.

Local and systemic humoral response to ovine mastitis caused by Staphylococcus epidermidis

Objectives:

Mastitis is responsible for a decrease in milk yield and quality. Disease control is vital for producers’ profit and for consumer’s welfare. This study aimed at investigating the immune response to Staphylococcus epidermidis intramammary infection.

Methods:

A total of 14 S. epidermidis isolates from milk collected from ewes with subclinical mastitis were used. Protein extracts were prepared and analysed by sodium dodecyl sulphate–polyacrylamide gel electrophoresis. Immunoblotting assay was performed for the detection of specific IgG and IgA in blood and milk from S. epidermidis mastitic ewes and from healthy animals.

Results:

The presence of pathogen-specific IgG was detected in blood of both infected and healthy animals. However, in milk, pathogen-specific IgG was only identified in infected animals, while IgA was found in both groups. Proteins with 59 and 43 kDa were recognized by all immunoglobulins screened in blood and milk provided by both healthy and mastitic ewes. In addition, in milk, IgG and IgA for proteins with 35 kDa were also detected.

Conclusion:

The results have lead to propose a theory for immunoglobulin dynamics in mammary gland’s defence: blood IgG1, specifically targeting intestinal antigens, is transported to the mammary gland with the main purpose of protecting the newborn, while IgG2 is specific for mammary pathogens and is transported to the mammary gland exclusively during inflammation. This study suggests that only local immunization should trigger IgG-producing cells in the mammary gland as a response to mastitis antigens. Moreover, IgA seems to be of crucial value for the defence of the ewe mammary gland, and stimulation strategies towards an increase in IgA should be addressed for mastitis prevention.