Extended Data Fig. 3. SYK hyperphosphorylation in human epithelial cells.

(a) SYK hyper-phosphorylation in intestinal tissue from Patient 1 compared to healthy controls. Double immunostaining of normal and p.S550Y SYK variant colon biopsy sections for pSYK (red), β-catenin (green) and merged dual labeling (yellow). The normal case demonstrated a distinctive glandular apical expression of pSYK. The fine apical signal almost reaches to the microvilli. Scattered infiltrated cells show pSYK staining in lamina propria. Unstained patches of glandular epithelium represent goblet cells. Immunostaining of β-catenin as a structural membrane marker indicates an organized glandular architecture in the normal colon section. Staining for pSYK was evident at the glandular epithelial base (membrane and cytoplasm) in colon sections of the patient. The β-catenin labeling in patient 1 intestinal biopsies presented a disorganized glandular architecture compared to the normal control. One representative image is shown out of 3 total images acquired. (b) Double immunostaining of pSYK and the myeloid marker CD68 in rectal and duodenal biopsy sections of Patient 1 illustrating strong pSYK expression in intestinal epithelial cells with moderate overlap with CD68⁺ myeloid cells. One representative image is shown out of 6 total images acquired from rectal biopsies and 4 images acquired from duodenal biopsies.