From the Guidelines
Children have higher lymphocyte percentages compared to adults due to their developing immune system, with lymphocytes making up 50-60% of white blood cells in children versus 20-40% in adults. This difference is attributed to the active response of children's immune systems to new pathogens and the production of lymphocytes to build immunological memory 1. As children are exposed to various antigens for the first time, their bodies produce more lymphocytes, and their bone marrow also produces lymphocytes at a higher rate to establish a robust immune system.
The thymus gland, responsible for T-lymphocyte maturation, is larger and more active during childhood, gradually shrinking after puberty 1. This physiological difference is completely normal and represents a healthy immune response in developing children. Studies have shown that total lymphocytes and absolute CD4+ cell counts are much higher in healthy infants and young children compared to healthy adults 1. For example, normal median CD4+ cell counts in healthy infants and children are 3,200/mm3 during the first 6 months of life, declining to 2,600/mm3 between 13-24 months of age, and to 1,700/mm3 by 2-6 years of age 1.
Key factors contributing to higher lymphocyte percentages in children include:
- Active immune system development and response to new pathogens
- Higher production of lymphocytes by the bone marrow
- Larger and more active thymus gland during childhood
- Establishment of immunological memory through exposure to various antigens. As children age, their lymphocyte percentages gradually decrease and approach adult levels, typically by late adolescence, reflecting the maturation of their immune system and the establishment of immunological memory 1.
From the Research
Lymphocyte Percentages in Children
- Children have higher lymphocyte percentages due to the natural development of their immune system, with studies showing that the percentage of total lymphocytes and absolute numbers of T and B cells decline with age 2, 3, 4.
- The percentages of T cells within the total lymphocyte population increase with age, in both CD4+ and CD8+ subsets, while the percentages of B and NK cells are higher in newborn infants than in adults 2.
- Age-related changes in lymphocyte subpopulations are significant, with CD4 and CD8 lymphocyte counts declining significantly with advancing age 3.
- Healthy children's CD4 lymphocyte counts are considerably higher than previously established adult values, making age an important consideration in the interpretation of lymphocyte subsets in children 3.
Factors Influencing Lymphocyte Percentages
- Geographical location can influence immune development in children, with some immune cell types showing an altered rate of development in children from different regions 5.
- Anemia can also impact lymphocyte percentages, with anemic children having lower frequencies of recent thymic emigrant T cells, isotype-switched memory B cells, and plasmablasts 5.
- The composition of the immune system in children is dynamically transformed during the first years of life, and is influenced by various factors including age, location, and anemia status 5.
Reference Values for Lymphocyte Subsets
- Establishing reliable reference values for lymphocyte subsets in children is crucial for the interpretation of immunophenotyping data, and can help inform vaccine design and patient management 6.
- Age-matched reference values for lymphocyte subsets can provide a valuable guideline for the interpretation of immunophenotype data in children 6.