• antistreptolysin O titer
• immune system
• inflammation
• obsessive-compulsive disorder

Obsessive-compulsive disorder (OCD) is a disabling mental condition usually characterized by early onset, with a lifetime prevalence of about 2-3% and a similar gender distribution amongst adults. In the last years, a large amount of research has focused on the detection of immunological abnormalities in OCD, while postulating an immuno-inflammatory model of the disorder, taking into account the involvement of peripheral biomarkers, maternal-fetal interactions, microglial activation, gut dysbiosis and autoimmunity. As regards the latter, pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections (PANDAS) has been representing the paradigm of an autoimmune model for OCD in children, however, autoimmune processes are widely documented also in adult patients. From a lifespan perspective, it is conceivable that infectious insults might favour not only the onset, but also the maintenance and the relapses of OCD in vulnerable subjects, thus influencing the trajectory of the disorder. The present study aimed at assessing the clinical features of OCD subjects who had been exposed to group A β-hemolytic Streptococcus (GABHS) infection. Fifty-two (M=33, F=19) patients displaying antistreptolysin O (ASO) titer positivity were recruited from a group of OCD adult outpatients. No patients showed present symptoms of pharyngotonsillitis. The diagnosis of OCD was carried out according to the fifth edition of the Diagnostic and Statistical Manual of mental disorder (DSM-5) criteria and the Structured Clinical Interview for DSM-5 (SCID-5). The Yale-Brown Obsessive-Compulsive Scale (Y-BOCS) was used to assess the OCD symptomatology. The presence of depression, as assessed by the Hamilton Depression Rating Scale (HDRS or HAM-D), represented an exclusion criteria. The subjects who were on regular medication for OCD at the moment of assessment had significantly lower ASO titers. The ASO titers were positively related to the number of white blood cells (WBCs) and to current lithium treatment. The neutrophil count and the body mass index had, respectively, a positive and a negative correlation with the "distress associated with obsessive thoughts" item. The number of neutrophils was also inversely correlated to the patients' age, while the lymphocyte count and the levels of homocysteine had negative correlations with the age of OCD onset. Consistently with the inflammatory model of psychiatric disorders, this study corroborates the common theory according to which beneficial effects of psychotropic compounds might be exerted also through an anti-inflammatory activity. Taken together, results seem to suggest that OCD subjects with ASO titer-positivity display a chronic inflammatory state, despite not showing symptoms of bacterial infections, with different immunological alterations being related to different symptom dimensions. These patients might benefit from the administration of antibiotics targeting the GABHS infection, which seems to be involved not only in the onset, but also in the maintenance of OCD and related conditions.