Immune system interaction

Innate immune system: (born with)

• Functions independently of previous exposure to organisms

• Includes barriers like the skin, mucus and epithelial linings, macrophages, and neutrophils

• Uses germline-encoded receptors to detect invaders

Toll-like receptors (TLRs): Saturated fatty acids can induce activation of several TLRs; unsaturated fatty acids inhibit these pathways. TLRs can sense when the body is being exposed to a pathological level of lipids, which may increase or decrease appetite

Adaptive immune system:

• Consists of B and T lymphocytes  (B=antibodies. T=fighting cells)
  

• Relies on specific recognition of antigens and immunological memory
  

• Will respond better and quicker when exposed to the same antigen again
  

• Transfer of immunological memory occurs because of colostrum, vaccination, or infection
  

• Uses somatically (body) generated receptors to detect invaders
  

A diet high in saturated fats may depress both of these systems and lead to an increased risk of infections and cancers

Testing for bacteria:

• Assessment of the bacterial components of the microbiota was traditionally done through culture

• This can be unreliable because of underestimation when trying to detect a bacterial population in billions of bacteria

PCR can be better to assess actual bacterial populations in the GI tract; however, it sometimes lacks information on important bacteria and whether the bacteria are functional

Bacterium Categories:

• Aerobic bacteria occur in higher proportions in the small intestine

• Anaerobic bacteria are most common in the large intestine

Primary bacteria in dogs and cats: Normal good microbiome

• Firmicutes spp. (~40%)

• Bacteroides spp. (~30%)

• Fusobacteria spp. (~30%)

Beneficial species include:

• Dogs: Enterococci spp., Lactic acid bacteria

Cats: Lactobacillus spp., Enterococcus spp., Bifidobacterium spp.

Other components to microbiota

• Archaea

• Viruses

• Fungi

• Parasites

• *These only contribute to 2–5% of the total DNA composition of the microbiota

Bacterial Composition — Balance and Early Life

• A balanced microbial ecosystem is crucial for the health of the animal

• Bacterial groups are most depleted after the production of SCFAs such as butyrate and acetate, which provide energy to enterocytes and colonocytes

• Establishing a resident microbiome early is important for preventing an inappropriate immune response against bacterial and food antigens 

This can be aided by animals consuming colostrum early on and exposure to the maternal microbiota during nursing and cleaning