Cerebrospinal fluid γδ T cell frequency is age‐related: a case–control study of 435 children with inflammatory and non‐inflammatory neurological disorders

Summary Studies of cerebrospinal fluid (CSF) γδ T cells in children are limited, due especially to the lack of control data. In adults, gamma/delta T cells (TCR‐γδ) residing in the intrathecal space are sometimes involved in neuroinflammation. To evaluate the possible role of γδ T cells in paediatric neuroinflammation, we immunophenotyped cerebrospinal fluid (CSF) and blood lymphocytes using flow cytometry in a case–control study of 100 children with non‐inflammatory neurological disorders (NIND), 312 with opsoclonus–myoclonus (OMS) and 23 with other inflammatory neurological disorders (OIND). In NIND, the negative correlation between CSF γδ T cell frequency and patient age was striking: median frequency of 27% in infants and 3·3% in teens. Interindividual variations were largest in the youngest. There was no gender effect. In all OMS, after correcting for age, only a small effect of OMS severity remained. Measurement of markers for γδ T cell activation [human leucocyte antigen D‐related (HLA‐DR)], maturation (CD45RA, CD45RO) or intracellular cytokine staining [interleukin (IL)‐4, interferon (IFN)‐γ] failed to discriminate OMS and NIND groups. Of seven OMS immunotherapies/combinations, none altered the frequency of total CSF γδ T cells or subsets significantly. In OIND, the CSF γδ T cell frequency was < 10% for single samples of other paraneoplastic disorders [anti‐neuronal nuclear antibody (ANNA)‐1, PCA‐1, teratoma‐associated syndrome], cerebellar ataxia (post‐infectious, ataxia‐telangiectasia), acute disseminated encephalomyelitis, neuroborreliosis and encephalitis. This study provides new insights into CSF γδ T cells in the paediatric population. Although their role in CSF remains elusive, the negative age correlation, resistance to immunotherapy and our age cut‐off references for NIND are important findings for the design of future paediatric studies.