Lack of evidence for the dichotomy of TH1 and TH2 predominance in HIV-infected individuals

The Th1-Th2 hypothesis of HIV infection: new insights

In their earlier, much quoted, viewpoint article, Mario Clerici and Gene Shearer examined the role of T helper 1 (Th1)- and Th2-type responses in immune dysregulation associated with human immunodeficiency virus (HIV) infection. In this article, they consider the complications of a Th1-Th2 model raised by the nomenclature, discuss the issue of cytokine production by non-T cells, and compare data obtained from T-cell clones with heterogeneous populations of leukocytes from patients. They define Th-cell responses and cytokine profiles as 'type 1' and 'type 2', and reemphasize the importance of strong cellular immune responses, along with the cytokines that augment and maintain such responses, in protective immunity against HIV infection and AIDS progression. Finally, they present a model of activation-induced, cytokine-modulated, programmed cell death as a major factor in the pathogenesis of HIV infection and AIDS.

Cytokine measurements and interpretation of cytokine assays in human disease

Cytokines are powerful mediator and communication molecules capable of regulating a wide spectrum of biologic functions, including immune responses. Although the role of cytokines in the pathogenesis of human disease is not yet understood, assays for cytokines have become a common feature in research and clinical laboratories. However, numerous pitfalls accompany measurements of cytokine levels in body fluids and of cytokine synthesis or gene expression in tissue. Interpretation of results obtained in cytokine assays, especially those performed with pathologic specimens, is fraught with difficulties. While cytokine assays are clearly of value in monitoring patients treated with recombinant cytokines or receiving anticytokine therapy, the clinical significance of cytokine assays is not yet fully established. In this review, some of the complexities associated with cytokine monitoring are discussed. The crucial importance of understanding cytokine biology for meaningful assay interpretation is emphasized.

Th1 versus Th2 responses in AIDS

During the past two years, a simple theory that seeks to explain what causes the progression of HIV-infected individuals to AIDS has been gaining support. The theory holds that HIV-infected people switch from a T-helper type 1 (Th1) to a T-helper type 2 (Th2) state as the disease progresses. However the experimental data do not support the concept that a Th1/Th2 switch occurs in the majority of HIV-infected subjects, although it is conceivable that HIV-infected individuals who mount sustained and chronic Th2-type responses, as a result of allergic disorders and helminthic infestations, may undergo more active HIV replication and therefore progress faster to full-blown disease.

Tracking HIV during disease progression

Several recent advances have been made in the delineation of the multiple pathogenic mechanisms involved in the progression of HIV disease. Included among these are the virological and immunological events associated with primary infection and the delineation of the role of lymphoid organs.