2 Immune System of Udder and Pathogenesis of Mastitis

Transcript

Hi Vets,

In the last class, we have seen about the Epidemiology of Mastitis.

In this lesson, that is in lesson-2, we will see about the Immune system of Udder and the Pathogenesis of Mastitis.

Historically the milk from the cow’s udder was thought to be sterile, but the evolution of the concept of Udder Microbiota has completely changed the thought, that the milk from the udder was sterile. because even in the normal milk, which doesn’t have any disease we could be able to isolate more than 250 strains of bacteria.

And among these Microbiota some are pathogenic, which may be harmful to the udder and others are actually beneficial, which may prevent the occurrence of Mastitis.

The Udder Microbiota can also be classified based on the niches, that is udder microbiota of the teat affects the udder microbiota of the teat canal and the milk itself.

So among the microbiota of the teat apex, teat canal, and the milk, the number of or the diversity of the microbiota is more in the teat canal, that is more than 165 strains have been isolated from the teat canal.

Among these, Lactobacilli and the Lactococcy, have the property of aggregation and they have hydrophobic property and colonizing properties. So with this, they could compete with the pathogens which try to colonize and infect the udder.

Coming to Mammary Gland Defense Mechanism; that can again be divided into the first line of defense mechanism, that is the Anatomical barrier, the second one is the Innate immune system of the udder, and the third one is the Recruitment of Neutrophils.

So the Anatomical defense barriers are actually considered as the first line of defense mechanism, which includes the Teat skin, Teat system, and Teat canal.

Actually, in Teat skin, the stratified squamous epithelium is covered with a layer of keratin, which prevents the colonization of bacteria.

The Teat canal is also lined by Keratin, and a thin layer of lipid forms the physical plug and prevents the entry of pathogens into the udder.

Any microorganism which tries to enter the Teat canal in between the milking, will be trapped by the keratin layer and they will be flushed out along with some layer of keratin, during the next milking and this is called as keratin flush.

Even if they escape this and ascend, they have to face the challenge of the rosette of sternberg which is a ring of neutrophils that will destroy this bacteria.

Coming to the Innate immune response; the macrophages located in the alveoli, sensitize the bacteria which are entering into the udder and they engulf the bacteria by a process called Phagocytosis and they shred them into pieces and release these pieces, which will be again sensitized by the neutrophils and the neutrophils will be recruited to that place which again destroys these pathogens.

Apart from this, udder has many antimicrobial peptides and glycoproteins, one among them is Lactoferrin whose iron-binding capacity is 300 times more than the transferring. Actually, it is having a bactericidal effect on Staphylococcus aureus and a bacteriostatic effect on E-coli. So having all these immune systems how a pathogen causes Mastitis, prepare loss of keratin layer and post milking dilatation of the teat canal, this facilitates the entry of microorganism into the udder.

So once the organisms enter into the udder, they are being facilitated by the udder environment. Even they get horizontal signaling from the udder microbiota which is already residing in the udder.

Next, some of the bacteria like staphylococcus aureus and even E-coli go for Biofilm formation and Internalization.

So during this process even if the macrophages engulf, they go for encapsulation and remain dormant and live in the macrophages and also release proteases and toxins like alpha and beta, which on one side destroy the antibodies and on the other side they damage the epithelial cells and get internalized into the epithelium, where they reside for a long time with low activity and they again cause chronic Mastitis in due course of time.

On the other side, the presence of pathogens is sensitized by the neutrophils and they enter into alveoli, while entering into the alveoli, they displace the secretory cells leading to increased somatic cell count in the milk.

Aggregation of these leukocytes and blood clotting factors forms clots, which abstract the flow of milk out of the udder and they also cause scar formation and proliferation of connective tissue. And in the first lesson we have also seen, that is the main reason for reduced conception rates in cattle, so that is due to the mechanism that bacterial invasion releases LPS that is lipopolysaccharides, which increases the level of cytokines, PGF2 alpha, and increased body temperature, which in turn reduces the level of GnRH, LH, estradiol, and progesterone, these changes are harmful to oozing maturation, ovulation, embryo implantation, and early embryonic development, this results in the decrease of reproductive efficiency of dairy cows.

So far we have seen about

• the Microbiota of the udder,
• the Defense mechanism of the udder, and
• Pathogenesis

In the next class, we will see about the Clinical signs and Diagnosis of Mastitis.

Thank you!