Better Understanding Calf Immunity

Background

Although the concept of immunity has been understood in a general sense for a long time, there are still a lot of unknowns in the area of innate immunity. Innate immunity is the immune system’s first response to potentially harmful foreign substances, including bacteria and viruses. There is an evolving area of research around how cells are trained to become immune or more responsive to certain pathogens. Some studies have focused on respiratory pathogens, but few have looked into training immune cells in the intestines. Better understanding of innate immunity in the intestines could mean giving cattle a better chance at fighting disease pressure by improving the immune responses from commercial vaccines which could reduce the number of sick animals and the over-use use of antibiotics and other costly treatments.

In previous studies, this group has shown that treating cattle with an injectable Johne’s disease vaccine increases innate immune cells in the intestine. This suggests that activating the innate immune system through vaccination could potentially reduce infection in that area. This study is looking into whether activating this system in juvenile calves will increase their immunity to certain infectious diseases at a point in a calf’s life where vaccines would likely be ineffective due to maternal immunity. This could be a valuable tool to cow-calf producers as a means to improve the prevention of diseases like Johne’s which infect calves in early calf-hood.

Objectives

• Determine if an injectable Mycobacterium paratuberculosis bacterin vaccine (Silirum®) or a commercial preparation of mycobacterial cell wall material (Immunocidin®) can train innate immunity in neonatal calves to improve immune responses.
• Determine if trained innate immune cells primed using Silirum® or Immunocidin® can occupy the ruminant small intestine and have an improved response to microbial pathogens.

What they DID

Eight- to thirteen-day old calves received either a placebo, Silirum® vaccine, or Immunocidin®. At two and four weeks post-vaccination, white blood cells were collected and re-stimulated in vitro with various pathogens to see if Silirum® and Immunocidin® vaccinated calves had an enhanced immune response compared to the calves who received the placebo.

Calves were then euthanized at four weeks post-vaccination to collect intestinal tissue in order to isolate intestinal immune cells. These intestinal immune cells were incubated in vitro with various pathogens to compare if the cells isolated from Silirum® and Immunocidin® vaccinated calves had a greater immune response compared to the placebo calves.

What They Learned

At two- and four-weeks post-vaccination, there was no enhanced immune response between the Silirum® and Immunocidin® vaccinated calves compared to the placebo group. However, some Immunocidin® vaccinated calves did show a greater response to microbial stimuli in white blood cells compared to the placebo calves. When the intestinal immune cells were examined, the team found that calves injected with the Silirum® vaccine had altered immune responses occurring in intestinal cells but rather than increasing the immune response, calves were found to have reduced immune responses in the intestines.

Despite Silirum® and Immunocidin® being derived from the same family of mycobacteria, they have different effects on the immune response in the white blood cells and in intestinal immune cells of juvenile calves. Therefore, selecting the right species of pathogen, is critical for obtaining an effective activator of innate immune cells in the blood and intestines to have an enhanced response to a specific disease. This research also validates that using an injectable vaccine is a feasible and accessible delivery route of vaccines or substances to modify intestinal immunity.

What it Means

Injection with Mycobacterium-derived products has the potential to alter the intestinal immune system in juvenile calves. This intestinal immune response can be adapted to respond to a broad-spectrum of pathogens. However, more studies should be conducted to determine if these responses actually increase protection and immunity against the disease the cells are being trained to defend against. Further, more testing of how can we increase the effectiveness of the immune responses in order to increase overall immunity of the individual animal would help to make this a useable practice on farm.