166 - GENETIC INSIGHTS INTO KAWASAKI DISEASE: FCGR2/3 LOCUS COPY NUMBER VARIATIONS AS KEY PLAYERS IN KAWASAKI DISEASE SUSCEPTIBILITY AND SEVERITY

Background: Kawasaki disease (KD) is an acute febrile systemic vasculitis that affects coronary arteries. Intravenous immunoglobulin (IVIg) is the standard of care for patients with KD.  The constant region, F_c region (fragment, crystallizable), of IgG mediates its effector functions through F_c  gamma receptors (F_cγRs). FCGR gene has been implicated as one of the candidate genes for susceptibility to KD. Altered F_cγR expression can have significant implications on response to IVIg. There is paucity of literature on role of FCGRs in susceptibility to KD as well as the effect of genetic polymorphisms on IVIg response and resistance.

The present work was designed to study the role of functionally relevant copy number region variations in the FCGR2/3 locus and characterize the surface expression of F_cγRII and F_cγRIII) on neutrophils, CD3+ T, CD19+B, CD14+monocytes and CD56+Natural killer cells in North Indian patients with KD.

Methods:

Patients with KD, diagnosed based on  American Heart Association (AHA) criteria 2017, and healthy controls  were enrolled for screening Copy Number Region Variations (CNRs) using Multiplex Ligation-dependent Probe Amplification (MLPA) assay, MRC Holland (Table1). Surface staining of F_cγRII and F_cγRIII pre and post IVIg was done using CD32 - PE , CD32B/C - Alexa Fluor 700, CD16 - BV421 antibodies. Cells were acquired on X-20 LSR Fortessa (BD Biosciences).

Results:

Copy Number Variation Regions (CNRs) identified as CNR1, CNR2, CNR3, CNR4 and CNR5 (Nagelkerke et al., 2015) (Moraru et al., 2021) were found in 22/70 (31.4%) patients. None of the controls tested revealed these variations. Patients with CNRs showed corroborative changes in surface expression of the receptors (Figure 1, 2).  On comparison of surface expression of F_cγ receptors [FcγRII (CD32 and FcγRIII (CD16)] on various immune cells before and after IVIg administration, percentage expression of FcγRIII on neutrophils and NK cells [CD16B and CD16A] was significantly decreased (p=0.008; 0.0013) prior to IVIg administration in patients when compared to healthy controls.  Patients with CNR2 duplication and CNR5 deletion showed poor response to IVIg and needed treatment intensification.

Conclusion: Patients with KD have CNVs in FCGR2/3 locus. Effect of  deletion or duplication in CNRs can be seen on surface expression of F_cγRs in patients with KD both before and after IVIg administration. CNRs in FCGRs may not only have role in pathogenesis but also can be predictors of IVIg response or resistance.