CHAGASIC PATIENTS LACK CD28 EXPRESSION ON MANY OF THEIR CIRCULATING T-LYMPHOCYTES

A balanced host-parasite interaction during Trypanosoma cruzi infectio n allows for the establishment of a chronic infection that can last fo r many years. T cells are a major element responsible for parasite spe cific and non-specific immunity during the complex immune response of the host. However, the subpopulations of T cells involved in the respo nse, as well as the exact mechanisms through which those cells are act ivated or rendered unresponsive, are not well defined. It is known tha t co-stimulatory signals, some of which are mediated via CD28, are of critical importance in the triggering of appropriate T cell responses. In this study the authors performed double-labelling studies to deter mine the frequency of expression of CD28 by CD4(+) and CD8(+) T lympho cytes in the peripheral blood of patients with Chagas' disease. The re sults show that chagasic patients throughout the spectrum of chronic c linical forms of the infection have significantly higher mean frequenc ies of CD4(+) CD28(-) and CD8 + CD28(-) T cells, as compared with non- chagasic individuals. Considering the importance of CD28 for T-cell ac tivation, the observed down-regulation or loss of CD28 during infectio n may indicate a possible basis for observed immunoregulatory events o r distinct stages of T-cell activation in this infection. Recent evide nce from patients with HIV/AIDS indicates that CD28(-) cell population s are more likely to undergo apoptosis, and increased apoptosis has be en observed in experimental Chagas disease.