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Marked increase in L-selectin-negative T cells in neonatal pertussis. The lymphocytosis explained?
1Department of Pathology, University of Texas Medical Branch, Galveston 77555-0741, USA.
Insights
Pertussis infection in a neonate caused a significant reduction in T-cell L-selectin expression. This likely impairs T-cell homing to lymph nodes, explaining the observed lymphocytosis in pertussis.
Area of Science:
- Immunology
- Pediatrics
- Infectious Diseases
Background:
- Pertussis (whooping cough) is a highly contagious respiratory infection.
- Lymphocytosis, an elevated lymphocyte count, is a characteristic finding in pertussis.
- Understanding lymphocyte behavior is crucial for managing infectious diseases in newborns.
Purpose of the Study:
- To detail the immunophenotype of peripheral blood lymphocytes in a neonate with pertussis.
- To compare these findings with cord blood from healthy newborns.
- To investigate the mechanism behind lymphocytosis in pertussis.
Main Methods:
- Flow cytometry was used to analyze peripheral blood lymphocytes from a pertussis-infected neonate.
- Immunophenotyping was performed on T cells (CD3+), B cells (CD19/20+), and NK cells (CD16/56+).
- Comparison was made with cord blood samples from healthy newborns.
Main Results:
- Neonate lymphocytes were predominantly CD3+ T cells (72%) with a normal CD4/CD8 ratio.
- T cells showed reduced HLA-DR and increased CD45RA expression, indicating a naive state.
- A striking deficiency in L-selectin (CD62L) expression was observed on T cells, particularly CD4+ T cells.
Conclusions:
- The reduced L-selectin expression on T cells in pertussis may inhibit their homing to lymph nodes.
- This impaired homing mechanism offers a potential explanation for the marked lymphocytosis seen in pertussis.
- Pertussis toxin might be responsible for inducing the observed reduction in L-selectin expression.
Abstract:
The detailed immunophenotype of peripheral blood lymphocytes from a neonate with pertussis was determined by flow cytometry and compared with results from cord blood from healthy newborns. Most (72%) of the lymphocytes were CD3+ T cells with a normal CD4/CD8 ratio (2.5). The T cells were largely HLA-DR negative and CD45RA+, consistent with unstimulated naïve T cells. Almost all of the CD4+ T cells were Leu8 (L-selectin, CD62L) negative, while almost all of the CD8+ T cells were CD28+. There was no increase in CD7- CD4+ T cells (Th2-like). No relative increase in CD16/56+ NK cells (5%) or CD19/20+ B cells was seen. The most dramatic finding in this case was the remarkable lack of expression of L-selectin by the T cells. L-selectin expression is associated with homing of peripheral blood lymphocytes to lymph nodes. The dramatic reduction in L-selectin expression of the T lymphocytes in pertussis, perhaps induced by pertussis toxin, likely prevents homing of the T cells to peripheral lymphoid tissues and provides a likely explanation for the marked lymphocytosis noted in this disease.