Nicotine, as a novel tolerogenic adjuvant, enhances the efficacy of immunotherapy in a mouse model of allergic asthma

An increasing trend in the incidence of allergic diseases including asthma and related morbidity
and mortality is observed worldwide during the last decades. Allergen-specific immunotherapy is suggested
for the treatment of some allergic diseases; nevertheless, there is always a menace of uncommon, but
life-treating reactions due to increasing the administration of allergen extract doses. Hence, improving
its efficacy may reduce the required doses as well as the risk of such reactions. The current study aimed
at examining the effects of nicotine (NIC), as a tolerogenic adjuvant, on the improvement of immunotherapy
efficacy in a mouse model of allergic asthma. BALB/c mice were sensitized using alum and ovalbumin
(OVA) on the days 0 and 7. Mice received OVA either alone or together with NIC (1 or 10 mg/kg)
on the days 21, 23, and 25. Then, the mice were challenged with OVA 5% using a nebulizer
on the days 35, 38, and 41 and sacrificed the next day. Co-administration of OVA and NIC decreased
the inflammation of the lung tissue, eosinophils count in the bronchoalveolar lavage (BAL) fluid, the serum
level of OVA-specific immunoglobulin E, as well as interleukin (IL)-4 production, while increasing
the population of antigen-specific regulatory T-cells (Treg cells) and transforming growth factor-β/IL-4
(TGF-β/IL-4) ratio compared to the OVA and control groups in a dose-dependent manner. Collectively,
the findings suggest that administration of NIC plus the allergen increased immunotherapy efficacy
through decreasing allergic inflammation and allergic responses intensity, and increasing
Treg cells population.