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Lymphocyte activation in HIV-1 infection. II. Functional defects of CD28- T cells
N J Borthwick1, M Bofill, W M Gombert
1Department of Clinical Immunology, Royal Free Hospital and School of Medicine, London, UK.
Insights
In HIV-1 infection, T cells lose CD28 expression, leading to an accumulation of unresponsive effector cells. This lack of CD28 impairs T cell activation and proliferation, contributing to immune dysfunction.
Area of Science:
- Immunology
- Virology
- Cell Biology
Background:
- CD28 is a crucial co-stimulatory molecule for T cell activation.
- HIV-1 infection is known to cause immune dysregulation and T cell dysfunction.
Purpose of the Study:
- To compare CD28 expression on T and NK cells in HIV-1-negative and HIV-1-positive individuals.
- To correlate CD28 expression with T cell activation and proliferative capacity in HIV-1 infection.
Main Methods:
- Multiparameter flow cytometry was used to analyze CD3, CD28, and other cell markers in peripheral blood.
- Cell proliferation and blast transformation were quantified after stimulation with mitogens like PHA and anti-CD3.
- CD28- cells were purified to confirm experimental observations.
Main Results:
- HIV-1-positive individuals showed significantly reduced CD28 expression on T cells, with an expansion of CD3+CD28- T cells.
- These CD3+CD28- T cells exhibited activation markers but were unresponsive to mitogens and failed to proliferate.
- A strong correlation was observed between lack of CD28 expression and poor T cell proliferation in HIV-1-positive individuals.
Conclusions:
- HIV-1 infection leads to the accumulation of activated but CD28- T cells, representing terminally differentiated effector cells.
- The absence of the CD28 co-stimulatory signal renders these T cells unresponsive to further stimulation.
- This CD28 deficiency contributes to impaired immune responses in HIV-1 infection.
Objectives And Design:
The expression of the accessory molecule CD28 was compared in various populations of T and natural killer (NK) cells from HIV-1-negative and HIV-1-positive individuals and correlated with activation using mitogens in vitro.
Methods:
Multiparameter flow cytometric analysis using combinations of CD3 CD28 and other markers was performed together with absolute cell counting in peripheral blood. Blast transformation and proliferative responses were also quantitated using the Cytoronabsolute after stimulation with phytohaemagglutinin (PHA) and anti-CD3. CD28- cells were also purified to confirm the observations.
Results:
In HIV-1-negative individuals > 90% of CD3+ T cells were CD28+ and responded to stimulation, while CD3- CD16+ CD57+ NK-like cells were CD28- and failed to respond. In HIV-1-positive individuals the expression of CD28 was greatly reduced and the proportion of CD3+CD28- T cells expanded. CD8 lymphocytosis was caused entirely by the accumulation of CD28- T cells and many of these expressed activation markers human lymphocyte antigen-DR, CD38 and CD45RO on their membrane and molecules such as TIA-1 and perforin, associated with cytolytic function, in their cytoplasm. The strong positive correlation (r = 0.66) between the lack of CD28 expression and the poor proliferation from HIV-1-positive individuals was confirmed by demonstrating that only CD28+ cells transformed into lymphoblasts and proliferated. Although the CD28- including CD3+ T cells transiently expressed CD25 (interleukin-2R alpha), they did not undergo blastogenesis or activation measured by bromodeoxyuridine uptake and died after 3-4 days in culture. These observations were confirmed in costimulation experiments with anti-CD2 and anti-CD28.
Conclusion:
In HIV-1 infection activated CD3+CD28- T cells accumulate but are unresponsive to mitogens and anti-CD28. These cells appear to represent terminally differentiated effector cells which fail to respond to further stimuli because of the absence of a CD28 second signal.