89 CHOLINERGIC STIMULI ENHANCE JEJUNAL MAST CELL RESPONSES TO LUMINAL ANTIGENS IN VITRO IN OVALBUMIN-SENSITIZED MICE

Abstract

Female BALB-C mice were sensitised to ovalbumin (OVA) by i.p. injection of 1 μg OVA in 0.5 ml PBS containing 1 mg alum and after 14 days boosted with i.p. 100 μg OVA in 0.5 ml PBS. Animals were sacrificed 10 days later. The jejunum was excised, stripped from muscle layers and mounted in Ussing chambers, transepithelial potential difference and resistance were recorded and equivalent short circuit current changes (ΔIsc) were calculated. All experiments were done in the presence of 10-6 M tetrodotoxin (serosal) to minimise endogenous neurotransmitter release. Serosal addition of 10-5 M OVA caused a maximal ΔIsc of 58.6 ± 6.0 μA/cm2 (n=5) after 2 minutes. Mucosal addition of 10-5 M OVA caused a maximal ΔIsc of 9.8 ± 2.2 μA/cm2 (n=7) after 7 minutes. In the presence of the cholinomimetic carbachol (10-5 M, serosal, added 30 minutes before OVA), ΔIsc after serosal addition of 10-5 M OVA was significantly reduced (p<0.002, t-test), maximal ΔIsc was 19.6 ± 5.7 μA/cm2 (n=4) after 2 minutes. In contrast, ΔIsc after mucosal addition of 10-5 M OVA in the presence of carbachol was significantly enhanced (p<0.02), maximal ΔIsc was 21.1 ± 4.0 μA/cm2 (n=6) after 7 minutes. The reduction in serosal OVA-evoked ΔIsc in the presence of carbachol may be explained by the finding that preincubation with preincubation with carbachol (maximal ΔIsc 96.1 ± 11.3 μA/cm2, n=14, return to baseline values in 30 minutes) decreased the ΔIsc evoked by histamine: maximal ΔIsc by serosal 10-4 M histamine (50.4 ± 6.5 μA/cm2, n=14) was significantly reduced to 31.1 ± 7.3 μA/cm2, n=7 (p<0.05), when added 30 minutes after carbachol. In the absence of carbachol the ΔIsc response to mucosal OVA was significantly (p<0.001) smaller then — and only 17% of — the ΔIsc induced by serosal OVA. In the presence of carbachol the ΔIsc response to mucosally added OVA was not different (p<0.90) from the ΔIsc response to serosally added OVA (100%). Thus, carbachol causes a 2- to 6-fold increase of anaphylactic mast cell responses to luminal OVA. We conclude that cholinergic stimulation, either via vagal nerve endings or via enteric interneurons may enhance small intestinal anaphylactic responses in sensitised mice, most probably by increasing the transepithelial passage of luminal antigens. We hypothesise that these findings may be of relevance in patients with food allergy.