title: Lymphocyte subpopulations in premature infants: an observational study.
abstract: OBJECTIVE
  The infant's immune system evolves over the first months and years of life. Strong correlation exists between lymphocyte count, lymphocyte subpopulations and gestational age at birth. Associations with antenatal and postnatal steroid treatment, infection and chronic lung disease have also been described. Few published studies report the effect of increasing postnatal age (PNA) and comorbidities on lymphocyte subpopulations in premature infants beyond the first 4 months of life. This study aimed to describe changes in lymphocyte subpopulations in preterm infants up to 13 months PNA.
  
  
  METHODS
  Premature infants (23-34 weeks completed gestation) from five centres had lymphocyte subpopulations measured at 2, 5 or 7, 12 and 13 months PNA alongside their vaccine responses in a vaccination trial.
  
  
  RESULTS
  393 blood samples from 151 babies were analysed. There was an increase in absolute numbers of total lymphocytes (median cell count 6.21×109/L at 13 months compared with 4.9×109/L at 2 months PNA) and CD3+, CD4+, CD8+, natural killer and B cells with increasing age. At 2 months PNA, there was a positive correlation between gestation and CD3+and CD4+counts (r=0.32 and 0.46, respectively) and proportions (r=0.22 and 0.41, respectively), and CD4+:CD8+ratios (r=0.57), but a negative correlation with CD8+proportions (r=-0.32).
  
  
  CONCLUSIONS
  This longitudinal study describes the distribution of lymphocyte subpopulations in premature infants and provides reference ranges for the major lymphocyte subsets to help guide clinicians when assessing premature infants for immunodeficiency in the first year of life.
  
  
  BACKGROUND
  EudraCT 2007-007535-23.
authors.affiliation: Paediatric Infectious Diseases Research Group and Vaccine Institute, St George's, University of London, London, UK.
authors.forename: Alison
authors.identifier: http://orcid.org/0000-0002-3196-2355
authors.initials: A
authors.lastname: Kent
authors.affiliation: Neonatal Unit, Queen Alexandra Hospital, Portsmouth, UK.
authors.forename: Tim
authors.initials: T
authors.lastname: Scorrer
authors.affiliation: Oxford Vaccine Group, University of Oxford, and the NIHR Oxford Biomedical Research Centre, Oxford, UK.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Pollard
authors.affiliation: Oxford Vaccine Group, University of Oxford, and the NIHR Oxford Biomedical Research Centre, Oxford, UK.
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Snape
authors.affiliation: Neonatal Unit, Norfolk and Norwich University Hospitals NHS Foundation Trust, Norwich, UK.
authors.forename: Paul
authors.initials: P
authors.lastname: Clarke
authors.affiliation: Neonatal Unit, Norfolk and Norwich University Hospitals NHS Foundation Trust, Norwich, UK.
authors.forename: Karen
authors.initials: K
authors.lastname: Few
authors.affiliation: Department of Paediatric Infectious Diseases, Evelina London Children's Hospital, London, UK.
authors.forename: Esse
authors.initials: E
authors.lastname: Menson
authors.affiliation: Department of Paediatric Allergy and Immunology, Royal Manchester Children's Hospital, Manchester, UK.
authors.forename: Anu S
authors.initials: AS
authors.lastname: Varghese
authors.affiliation: Department of Paediatric Allergy and Immunology, Royal Manchester Children's Hospital, Manchester, UK.
authors.forename: Stephen
authors.initials: S
authors.lastname: Hughes
authors.affiliation: Paediatric Infectious Diseases Research Group and Vaccine Institute, St George's, University of London, London, UK.|Immunisation, Hepatitis and Blood Safety Department, Public Health England, Colindale, London, UK.
authors.forename: Shamez N
authors.initials: SN
authors.lastname: Ladhani
authors.affiliation: Paediatric Infectious Diseases Research Group and Vaccine Institute, St George's, University of London, London, UK.
authors.forename: Paul T
authors.initials: PT
authors.lastname: Heath
keywords: Immunology; Infectious Diseases; Neonatology