CD80/CD28 co-stimulation in human brucellosis

Abstract

Summary Despite treatment, 10–30% of brucellosis patients develop chronic disease, characterized by atypical clinical picture and/or relapses. A defective T helper 1 (Th1) response and a long percentage of CD4+/CD25+ cells have been described in chronic brucellosis patients. CD80/CD28 co-stimulation is critical for an efficient Th1 response and has not been studied previously in human brucellosis. In order to investigate the role of CD80/CD28 co-stimulation, 13 acute brucellosis patients (AB), 22 chronic brucellosis patients (CB, 12/22 relapsing type-CB1 and 10/22 atypical type-CB2), 11 ‘cured’ subjects and 15 healthy volunteers (controls) were studied. The percentage of CD4+/CD28+ T lymphocytes and CD14+/CD80+ monocytes were analysed by flow cytometry both ex vivo and after phytohaemagglutinin (PHA)-stimulation with or without heat-killed Brucella abortus (HkBA). Ex vivo analysis showed no differences between all groups studied. PHA stimulation up-regulated the percentage of CD80+ monocytes in AB compared to ‘cured’ subjects and controls (P < 0·001), although the proportion of CD4+/CD28+ cells did not alter. A higher percentage of CD80+ monocytes was observed in the CB1 subgroup, compared to AB, ‘cured’ subjects and controls (P = 0·042, < 0·001 and < 0·001, respectively). CB2 was characterized by a lower percentage of CD80+ monocytes in comparison to CB1 (P = 0·020). HkBA in PHA cultures down-regulated the percentage of CD80+ monocytes compared to PHA alone in all groups, especially in AB and CB patients (P < 0·001 and P = 0·007, respectively). In conclusion, the diminished percentage of CD4+/CD25+ T cells in CB is not associated with inadequate CD80/CD28 co-stimulation. We speculate that differential frequency of CD80+ monocytes after PHA stimulation could serve as a qualitative parameter of disease status, related to the different clinical forms of chronic brucellosis.