Related Experiment Videos
In situ activation of helper T cells in the lung
1Division of Pulmonary and Critical Care Medicine, Department of Medicine, New York University School of Medicine, New York, New York 10016, USA.
Insights
Helper T cells in the lungs of tuberculosis patients show a unique mix of naive and memory markers, alongside early and late activation signals. This distinct phenotype may be crucial for understanding the immune response to Mycobacterium tuberculosis.
Area of Science:
- Immunology
- Cellular Biology
- Respiratory Medicine
Background:
- Helper T cells are crucial for adaptive immunity, particularly in response to Mycobacterium tuberculosis (TB).
- Understanding T cell responses in the lung versus peripheral blood is key to deciphering TB immunity.
Purpose of the Study:
- To investigate the surface phenotype of CD4(+) helper T cells in bronchoalveolar lavage (BAL) fluid compared to peripheral blood (PB) in individuals with and without TB.
- To identify unique T cell populations in the lung that may mediate memory immunity to TB.
Main Methods:
- Utilized three- and four-color flow cytometry to analyze surface markers on CD4(+) lymphocytes.
- Collected BAL and PB samples from TB-infected, purified-protein-derivative-negative, and purified-protein-derivative-positive subjects.
Main Results:
- CD4(+) lymphocytes in BAL fluid paradoxically coexpressed naive (CD45RA) and memory (CD45RO) markers, unlike those in PB.
- A significantly higher proportion of BAL CD4(+) lymphocytes expressed the early activation marker CD69 compared to PB.
- A distinct minor population of CD69(bright) CD25(bright) CD4(+) lymphocytes was identified in BAL but not PB.
Conclusions:
- Lung CD4(+) lymphocytes exhibit an unusual co-expression of naive, memory, and activation markers, suggesting a specialized role in the pulmonary immune response.
- These findings highlight the importance of studying lung-resident T cells for understanding TB immunity and evaluating potential TB vaccines.
Abstract:
To better understand the lung and systemic responses of helper T cells mediating memory immunity to Mycobacterium tuberculosis, we used three- and four-color flow cytometry to study the surface phenotype of CD4(+) lymphocytes. Bronchoalveolar lavage (BAL) fluid and peripheral blood (PB) samples were obtained from a total of 25 subjects, including 10 tuberculosis (TB)-infected subjects, 8 purified-protein-derivative-negative subjects, and 7 purified-protein-derivative-positive subjects. In marked contrast to CD4(+) lymphocytes from PB (9% +/- 5% expressing CD45RA and CD29), the majority (55% +/- 16%) of CD4(+) lymphocytes in BAL (ALs) simultaneously expressed CD45RA, a naïve T-cell marker, and CD29, members of the very late activation family. Further evaluation revealed that CD4(+) ALs expressed both CD45RA and CD45RO, a memory T-cell marker. In addition, the proportion of CD4(+) lymphocytes expressing CD69, an early activation marker, was drastically increased in BAL fluid (83% +/- 9%) compared to PB (1% +/- 1%), whereas no significant difference was seen in the expression of CD25, the low-affinity interleukin 2 receptor (34% +/- 15% versus 40% +/- 16%). More importantly, we identified a minor population of CD69(bright) CD25(bright) CD4(+) lymphocytes in BAL (10% +/- 6%) that were consistently absent from PB (1% +/- 1%). Thus, CD4(+) lymphocytes in the lung paradoxically coexpress surface molecules characteristic of naïve and memory helper T cells as well as surface molecules commonly associated with early and late stages of activation. No difference was observed for ALs obtained from TB-infected and uninfected lung segments in this regard. It remains to be determined if these surface molecules are induced by the alveolar environment or if CD4(+) lymphocytes coexpressing this unusual combination of surface molecules are selectively recruited from the circulation. Our data suggest that ex vivo experiments on helper T-cell subsets that display distinctive phenotypes may be pivotal to studies on the human immune response to potential TB vaccines.