Characterization of IgE-mediated cutaneous immediate and late-phase reactions in nonallergic horses.

This research study involved examining the skin response of nonallergic horses after injections of a specific type of antibody. The results suggest this method could be used for assessing allergic skin diseases in horses.

Methodology

• 6 healthy horses were selected for the experiment. Their skin in the cervical (neck) area was injected with two types of substances- polyclonal rabbit anti-canine IgE (anti-IgE) and rabbit IgG. These are essentially antibodies made by rabbits.
• The research team then took measurements of wheals (swelling caused by skin inflammation) and skin biopsy specimens before the injection and also 20 minutes, 6 hours, 24 hours, and 48 hours post-injection.
• The tissue sections obtained from the biopsies were evaluated for the presence of inflammatory cells at four different dermal (skin) depths. The team also performed immunohistochemical analysis for CD3, CD4, and CD8 cells (these are types of T cells involved in immune response).

Results

• They found that the wheals caused by the anti-IgE were significantly larger than those caused by the IgG at 20 minutes, 6 hours, and 24 hours post-injection.
• It was also observed that there were significantly more degranulated mast cells (cells that play a crucial role in allergic responses) following anti-IgE injection than after IgG injection.
• Similarly, notably more eosinophils (a type of white blood cell) were present at the 6, 24, and 48 hour marks and more neutrophils (another type of white blood cell) at 6 hours after injecting anti-IgE, compared with the cell numbers at the same timeframes after administering IgG.
• Furthermore, they observed a higher number of eosinophils in the deeper layers of skin after anti-IgE injections when compared with the results for IgG injections.
• Contrarily, they did not find any significant differences in the numbers of CD3(+), CD4(+), or CD8(+) cells between the two treatments. This suggests that T cell involvement was not significantly different whether anti-IgE or IgG was injected.

Conclusions

• The team concluded that injecting anti-IgE antibodies caused both visible and microscopic inflammation in the horses’ skin, which was characterized most notably by mast cell degranulation and an increased presence of eosinophils and neutrophils.
• Interestingly, this pattern is similar to what is seen in horses with naturally occurring allergic skin diseases. However, unlike natural allergies, they did not observe an increase in lymphocytes (a type of white blood cell) with the injections.
• These findings suggest that intradermal injection of anti-IgE might be a useful method for simulating and studying allergic skin conditions in horses, in a controlled study environment.