In the diagnosis of liver disorders, a liver biopsy is a gold standard. However, it leaves limited room for extensive immunological profiling of the liver. As a result, for a study, researchers investigated whether fine needle aspirates (FNAs) might be utilized to investigate hepatic immunity in children. They included 74 children who had diagnostic (n=17) or procedure (n=57) biopsies after a liver transplant (LT). FNAs and matched blood were collected. In addition, explant liver tissue was obtained from 14 children undergoing LT. Immune cells were extracted from peripheral blood, FNAs, and liver transplants. Flow cytometry was used to profile the immune phenotypes. 

Biopsied patients (58%) had a median age of 46 months (interquartile range [IQR]: 12–118), while LT patients (71%) had a median age of 48 months (IQR: 21–134, P=0.78). CD69+, a marker of tissue-resident immune cells, was found in 1.3% of CD3+ T cells from blood, but it was greater in FNA (20%) and tissue (49%, P<0.001). CD4+ T-cell frequencies in tissue (13%) and FNAs (20%) were lower than in blood (35%) (P<0.001), although CD8+ T-cell frequencies in tissue (33.5%) and FNA (32%) were greater than in blood (25%) (P<0.01). When compared to blood (1.7%, P<0.001), mucosal-related invariant T lymphocytes were enriched in liver tissue (8.8%) and FNA (4.4%). In both FNA and explant, the proportion of total Tregs (CD4+CD25+FOXP3+CD127low/-) fell while the proportion of activated Tregs (CD4+CD45RA-FOXP3high) rose. The frequencies of Breg (CD19+CD20+CD24highCD38high) were comparable across all groups. FNA was a feasible approach for collecting small cell subsets such as regulatory T/B cells from the hepatic immune system.