Chronic immune activation associated with intestinal helminth infections results in impaired signal transduction and anergy

Abstract

Helminthic parasites cause widespread, persistent infections in humans. The immigration of Ethiopians to Israel (a group denoted here by "Eth."), many of them infested with helminths and in a chronic immune-activation state, enabled us to investigate the effects of such immune activation on immune responses. We studied the immune profile and immune functions of 190 Eth. and Israeli non-Eth. (Isr.) highly, partially, or non-immune-activated individuals. Immune cells from highly immune-activated individuals were defective in several signaling responses, all of which were restored gradually following anti-helminthic treatment. These cells showed poor transmembrane signaling, as seen by the phosphorylation of various tyrosine kinases and of the MAPK kinases, ERK1/2 and p38; deficient degradation of phosphorylated IkappaBalpha; increased expression of cytotoxic T lymphocyte-associated antigen 4 (CTLA-4), which appears to block proliferative responses in these cells; decreased beta-chemokine secretion by CD8(+) cells after stimulation; and reduced proliferation to recall antigen stimulation. Highly immune-activated individuals also showed decreased delayed-type skin hypersensitivity responses to recall antigen before deworming. These findings support the notion that chronic helminthic infections cause persistent immune activation that results in hyporesponsiveness and anergy. Such impaired immune functions may diminish the capacity of these individuals to cope with infections and to generate cellular protective immunity after vaccination.

Figure 1

Correlations between the percentage of HLA-DR⁺CD4⁺ cells and other cell subsets in Eth. individuals. ns, not significant.

Figure 2

Attenuated phosphorylation of ERK1 and ERK2 in chronically immune-activated individuals, as determined by Western blot analysis. PBMC extracts obtained from nonactivated (NA), highly activated (HA), or partially activated (PA) Eth. or Isr. individuals were stimulated for 0 or 6 minutes (a) or for 0, 3, 6, 12, and 18 minutes (b) with PMA and CA²⁺ ionophore. Lysates of these cells were resolved on SDS-PAGE and immunoblotted with anti-phosphorylated p42/44 MAPK/ERK Ab (1:10,000) and anti-BCL2 Ab (1:500). The immunoblot in b was stripped and rehybridized with anti-p42/44 MAPK/ERK Ab (1:10,000). pERK, phosphorylated ERK.

Figure 3

Impaired activation of IκBα and p38 in highly immune-activated individuals. PBMC extracts obtained from nonactivated (NA) Isr. and highly activated (HA) Eth. individuals were stimulated for 0 or 15 minutes with PMA and CA²⁺ ionophore. Lysates of these cells were resolved on SDS-PAGE and immunoblotted with (a) anti-IκBα (1:2,500) or with (b) anti-diphosphorylated p38 MAP kinase (1:1,000). (c) Kinetic analyses of the changes in p38 phosphorylation and dephosphorylation after stimulation. The cells were stimulated with PMA and CA²⁺ ionophore for 0, 3, 6, or 12 minutes. As control, we activated jurkat cells.

Figure 4

Differential changes in tyrosine phosphorylation in chronically immune-activated individuals compared with nonactivated controls. The patterns of tyrosine phosphorylation in PBMC cells were determined at various times after stimulation of the cells with PMA and CA²⁺ ionophore. Although after stimulation, clear changes in the tyrosine phosphorylation pattern occurred in NA individuals, no significant changes were noted in the activated individuals.

Figure 5

(a) Diminished proliferation to PPD antigen by cells obtained from HA individuals. PBMCs were incubated for 6 days with or without 5 μg/ml PPD and then pulsed with [³H]thymidine. The log of SI (stimulation index: incorporation of [³H]thymidine in the presence of PPD divided by the amount of [³H]thymidine incorporated in the presence of medium alone) is plotted against the log of percentage of HLA-DR expression on the CD3⁺ cells. (b) Enhancement of proliferation to PPD after blockage of CTLA-4. PBMCs were stimulated with PPD (as in a, above) in the presence of 0.13 μg (0.66 μg/ml) Fab mAb against CTLA-4 or matched Fab isotype mAb control. The stimulation index results are the average of triplicates.