Microglia as a Target of Immunomodulation in Pediatric Autoimmune Neuropsychiatric Disorders associated with Streptococcal Infections (PANDAS)
Authors: Harris Delaney , Dutta Dey Pujarini , Sheikh Irshad A. , Daines Michael , Rice Sydney , Pedrosa Erica , Lachman Herbert 
Published: May 2024

PANDAS, or Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal Infections, is a neuropsychiatric condition characterized by the abrupt onset of diverse neuropsychiatric manifestations following streptococcal infections in children. It's believed to involve immune dysregulation and autoimmune targeting of the brain basal ganglia. However, the precise mechanisms remain unclear. Hypothesis: considering the role of microglia in neuroinflammation, evidence for their activation in PET imaging of PANDAS patients, and increased number of CD68+/Iba1+ activated microglia in mice inoculated with group A Streptococcus (GAS), we hypothesized that as a consequence of disrupted blood-brain barrier (BBB), circulating factors modulate microglial functions towards a pro-inflammatory phenotype. Methods: Untargeted metabolomics was performed with sera from 10 children with PANDAS and 12 healthy controls. Human iPSC-derived microglia were generated and exposed to 5% serum from PANDAS patients or healthy controls in the presence or absence of Polymyxin B (PMB; endotoxin scavenger) and assessed for nitric oxide (NOx) production, immunophenotyped with flow cytometry (TMEM119, TREM2, CD68, and Iba-1) and bulk RNA-seq analysis. Results: Significant differences in serum metabolomic profile of PANDAS cases were observed, particularly in pathways associated with amino acid, fatty acid, lipid, steroid, and oxidative stress-related pathways. Treatment of iPSC-derived or primary human microglia with PANDAS serum led to a significant increase in NOx production, which was blunted by approx. 30% by PMB. Immunophenotyping revealed a significant reduction in homeostatic markers TMEM119 and TREM2, and expansion of CD68+ and Iba-1+ microglia associated with inflammatory response. Regulation of TMEM119 and TREM2 was endotoxin-independent, while PMB partially blunted the increase in CD68 and Iba-1. RNAseq revealed dramatic effects of PANDAS sera on microglial gene expression pattern, with upregulated genes associated with C-type lectin receptor, TLR, TNF, and NFk-B signaling pathways among others. Conclusion: The results suggest that as a result of BBB disruption in PANDAS, associated systemic inflammatory mediators modulate the phenotype and function of the brain microglia, a mechanism that likely contributes to neuroinflammation and the observed symptoms. The observed contribution of endotoxin may also suggest a dysfunction of intestinal barrier which may compound the systemic immune responses in PANDAS. Arizona Department of Health Services RFGA2022-010-23 (PK) & ADHS17-00007403 (SR, MD); The Alex Manfull Fund (PK). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.