S1PR1 and hematocrit: In the autoimmune milieu of HT, this process is markedly amplified by upregulation of the S1P receptor 1 (S1PR1), as demonstrated in autoimmune thyroiditis models, where S1PR1 expression serves as a pivotal mediator of S1P-induced activation of signal transducer and activator of transcription 3 (STAT3) [18].