Deficient saliva-induced NETosis in response to saliva from patients with recurrent aphthous stomatitis due to loss of saliva sialyl Lewis^X. Neutrophils were stimulated to NETosis and examined by immunofluorescence microscopy and NET formation quantified as described in “Materials and methods.” Representative images are shown in supplementary Figure 7. (A) Neutrophils were stimulated with saliva from a person with recurrent aphthous stomatitis. Saliva was collected from a nonaphthous period, just prior to ulceration, from a period with ulceration, and during the recovery phase in which ulcers were still present. Error bars indicate standard deviation between 20 random images taken from each condition. Representative images and data from another person with recurrent aphthous ulcers are shown in supplementary Figure 7. (B) Western blot of sialyl Lewis^X in saliva from patient with recurrent aphthous stomatitis. (C) NETosis of neutrophils stimulated with saliva from healthy donor and saliva, buffer changed saliva, and mucins resuspended in protein-free saliva from a patient with recurrent aphthous stomatitis during the aphthous phase. N.S., not significant. *P < .05.