Assessing changes in serum IgG subclass antibodies in horses following a Phase I clinical trial of Antigen Specific Oral Immunotherapy of Culicoides spp. salivary gland proteins.

Abstract

Insect Bite Hypersensitivity has been extensively demonstrated as a IgE mediated Type I hypersensitivity caused by biting insects of Culicoides spp. in horses. The horse has the most IgG subclasses of any studied mammalian species, but their individual functions are not fully known. The blocking activity of human IgG4 in allergy provided the aim of this study to determine any changes in serum IgG subclass antibody levels after a phase I oral immunotherapy trial of common midge salivary gland proteins. This phase I trial took place over a period of 2 years. In the first year, 10 horses (cohort 1) were blood sampled, then 5 received a 1nMol immunotherapy dose containing the most allergenic midge salivary gland proteins, while the remaining 5 received a placebo dose (0nMol). Doses were given bi-weekly for 3 months before the cohort were re-blood-sampled. In the second year, 20 horses (cohort 2) were blood sampled. 5 received the placebo dose, with the remaining 15 receiving a 2nMol immunotherapy dose containing the most allergenic midge salivary gland proteins. After a month, 10 receiving the 2nMol dose moved up to a 4nMol dose, then after a further month, 5 receiving the 4nMol dose moved up to an 8nMol dose leaving 5 horses in each dosage group for one month. Dosing was once again performed bi-weekly, and blood sampling was performed at the conclusion of the immunotherapy. The sera collected was analysed for IgG1, IgG4/7, IgG5, IgG6, and IgE binding to 30 recombinant Culicoides spp. salivary gland proteins via indirect ELISA. Individual ODs were totalled, and the ratios calculated by dividing post-treatment sera by pre-treatment sera to obtain a single figure. These figures were analysed using a Kruskal Wallace test or a Mann-Whitney U test. Year 1 horses for IgE antibody levels demonstrated a significant difference (P=0.05) and year 1 horses for IgG1 demonstrated a borderline significance (P=0.0548). The other subclasses apart from IgG6 may have showed a dose effect. This study demonstrated that the administration of oral immunotherapy is safe in horses, as none of the measured adverse reactions (lip smacking, chewing and tongue movements, swelling of the tongue, urticaria (hives), and anaphylactic shock) were observed. It also demonstrates that equine serum IgE antibody levels are influenced by oral immunotherapy and may influence serum IgG subclass antibody levels.

Date of Award	3 Oct 2023
Original language	English
Awarding Institution	University of Bristol
Supervisor	Doug Wilson (Supervisor) & Tristan A Cogan (Supervisor)