Oral administration of Ag suppresses Ag-induced allergic conjunctivitis in mice: critical timing and dose of Ag.

BACKGROUND/AIMS: To investigate the effect of Ag doses and administration time points on oral tolerance induction in experimental allergic conjunctivitis (EAC).

METHODS: BALB/c mice were actively sensitised twice with ovalbumin (OVA) in alum, and then challenged twice with OVA in eye drops. Twenty minutes after the last challenge, the clinical appearance was evaluated. Twenty-four hours later, the conjunctivas, spleens and blood were collected for histological analyses, cytokine production assays, and measurement of serum Ig levels, respectively. The mice were fed with a high or low dose of OVA before sensitisation (prophylactic treatment). To assess the effect of therapeutic treatment, the high-dose Ag was administered after sensitisation. Control groups received phosphate-buffered saline without OVA. To determine the role of interleukin-10 (IL-10) and transforming growth factor-β (TGF-β) in prophylactic low-dose oral tolerance, mice were injected intraperitoneally with neutralising antibodies during the entire experimental period. To assess the role of regulatory T cells, neonatally thymectomised mice were injected with depleting anti-CD25 monoclonal antibodies before the low-dose prophylactic treatment.

RESULTS: OVA-feeding was suppressive even when the mice were treated soon after Ag sensitisation. Both the low and high doses of oral OVA suppressed EAC. High-dose treatment significantly suppressed EAC-related cytokine production and serum Ig levels. IL-10 and TGF-β were less likely to be involved in prophylactic low-dose oral tolerance induction but regulatory T cells played a role.

CONCLUSIONS: Prophylactic and early therapeutic treatment of OVA feeding suppressed EAC. Both high and low doses of oral OVA induced oral tolerance but with different mechanisms.