An alternative view of the Th1/Th2 switch hypothesis in HIV infection.
A theory that seeks to explain what induces the relentless progression of HIV-infected subjects to AIDS has received considerable attention. This theory holds that HIV infection results in a Th1/Th2 switch. However, analysis of constitutive cytokine mRNA expression in lymphoid tissues from HIV-infected individuals did not confirm an in vivo Th1/Th2 switch. Moreover, data available at the level of in vitro-stimulated peripheral blood mononuclear cells or cloned T cells do not provide clear evidence for a definite switch to the Th2 responses in any HIV-infected subject and in any phase of HIV infection. At most, currently available data on the profile of cytokines released in response to in vitro stimulation suggest a Th1-to-Th0 shift in a proportion of memory CD4+ T cells. On the other hand, experiments of in vitro infection with HIV of already established CD4+ T cell clones indicated that Th2 and Th0 cells support HIV replication better than Th1 cells, suggesting that early destruction of Th2 cells by direct or indirect HIV-mediated cell killing may occur. Finally, in some HIV-infected individuals with low CD4+ T cell counts, a prevalence of CD8+ T cells producing type 2 cytokines was found in both peripheral blood and skin. Thus, although the induction of a general Th2 state in HIV infection is not proven, enhanced production of type 2 cytokines may occur in a proportion of HIV-infected individuals and play some role in the pathogenesis of the disease.
Romagnani
S
S
Division of Allergology and Clinical Immunology, Istituto di Clinica Medica III, University of Florence, Italy.
Maggi
E
E
Del Prete
G
G
D000163:Acquired Immunodeficiency Syndrome / Q000209:etiology; D016207:Cytokines / Q000096:biosynthesis; D006678:HIV / Q000502:physiology; D015658:HIV Infections / Q000276:immunology* / Q000382:microbiology; D006801:Humans; D008954:Models, Biological; D018417:Th1 Cells / Q000276:immunology* / Q000382:microbiology; D018418:Th2 Cells / Q000276:immunology* / Q000382:microbiology; D014779:Virus Replication
D016207:Cytokines