19 - ANTIBODIES PRODUCED BY CHILDREN WITH KD CONSISTENTLY RECOGNIZE ANTIGEN IN KD TISSUES FROM THE US AND JAPAN

Background/Aim. We reported that synthetic antibodies generated from immunoglobulin sequences derived from patients with KD recognize an antigen in ciliated bronchial epithelium and coronary arteries of fatal cases.  The synthetic antibodies were derived from IgA antibodies present in coronary artery tissues from one patient with fatal KD (JID 2004;190:856-65) and derived from circulating IgA and IgG plasmablasts from 9 of 11 children presenting with acute KD (JID 2020;222:158-68). Here, we describe additional studies that extend these findings.

Methods: Monoclonal antibodies were produced from circulating plasmablasts from children with acute KD by cloning their immunoglobulin sequences into expression vectors and co-transfecting the light and heavy chains in 293F cells. Immunohistochemistry was performed with rabbit immunoglobulin versions of the antibodies on acute KD formalin-fixed, paraffin-embedded (FFPE) tissues from fatal KD cases from the US and Japan.

Results: We produced additional monoclonal antibodies from circulating plasmablasts from 12 patients with acute KD at our hospital and used them in immunohistochemistry assays on KD and control tissues. KD antigen was consistently detected in tissue from fatal KD cases using multiple antibodies from each of the 12 children. The antigen was identified in lung tissues from all of 10 US and 10 Japanese KD cases who died within the first month after fever onset and was absent in controls who died of RSV or influenza. When lymph node tissue adjacent to the lung was available, antigen was detected in cytoplasm of cells with the morphology of macrophages.

Conclusion: The consistent detection of KD antigen in fatal KD cases from the US and Japan targeted by antibodies produced by children with acute KD strongly supports the importance of this antigen in KD pathogenesis. Its localization to bronchial epithelium and adjacent lymph node tissues strongly suggests that KD antigen is a protein derived from a novel respiratory pathogen common to KD patients that undergoes antigen processing in draining lymph nodes before travelling in macrophages to the coronary arteries and damaging them. Given the rarity of fatal cases and the fact that most tissue from fatal cases is FFPE, the exact identification of the antigen has been very difficult, although an epitope/mimotope of the antigen has been identified. Continued efforts to identify this antigen should be a major focus of KD researchers in the future because they likely offer the best opportunity for elucidating the etiologic agent of KD, the most pressing research goal in the field.