Th1-driven immune reconstitution disease in Mycobacterium avium-infected mice

Opportunistic infection-associated immune reconstitution syndrome in transplant recipients

Reversal of pathogen-induced immunosuppression upon employment of effective antimicrobial therapy and withdrawal of iatrogenic immunosuppression has the potential to shift the host immune repertoire towards pathologic inflammatory responses conducive to immune reconstitution syndrome (IRS). Posttransplant IRS has been observed with fungi, M. tuberculosis, cytomegalovirus, and polyoma virus nephropathy. This review discusses the existing state of knowledge regarding IRS and the immune mechanisms that underlie its pathogenesis, with significant implications for developing reliable diagnostic biomarkers and optimal management strategies for post-transplant opportunistic infection-associated IRS.

TLR2-induced cytokine responses may characterize HIV-infected patients experiencing mycobacterial immune restoration disease

OBJECTIVES

Most HIV patients who experience Mycobacterium tuberculosis-associated immune restoration disease (TB IRD) display elevated interferon-gamma (IFNγ) responses against mycobacterial antigens, but these can occur without an IRD. Recognition of mycobacteria-associated molecular patterns through toll-like receptors (TLRs) on dendritic cells and monocytes induces cytokine production. Here, we investigate TLR-induced responses in IRD.

DESIGN

Peripheral blood mononuclear cells (PBMCs) were collected at approximately weeks 0, 6, 12, 24 and 48 after antiretroviral therapy from five patients experiencing TB IRD, nine matched non-IRD patients and 15 healthy controls.

METHODS

IFNγ production by PBMC stimulated with protein purified derivative (PPD) was assessed by ELISpot. TLR2 expression on myeloid dendritic cells (mDCs) and monocytes was assessed by flow cytometry. TNFα, IL-12p40 and IL-10 were measured by ELISA in 24-h cultures of PBMC with lipomannan (mycobacteria-derived TLR2 agonist).

RESULTS

TLR2 expression on mDC and monocytes was higher in patients than controls at baseline (P < 0.005). TLR2 expression decreased to normal levels on mDC by week 12, but remained higher on monocytes at week 24 (P = 0.02). At week 24, IRD patients showed higher IFNγ responses to PPD (P = 0.02), TLR2 expression on monocytes (P = 0.006) and lipomannan-induced TNFα production (P = 0.016) than non-IRD patients. Lipomannan-induced TNFα and IL-12p40 responses paralleled TB IRD in the patients with high TLR2 expression. IL-10 levels did not associate with IRD.

CONCLUSION

TLR2-induced pro-inflammatory cytokines by dendritic cells or monocytes may contribute to the pathogenesis of mycobacterial IRD.

Development of cytomegalovirus (CMV) immune recovery uveitis is associated with Th17 cell depletion and poor systemic CMV-specific T cell responses

We tested whether impaired systemic immunoregulation and hyperactive immune responses are associated with an immune reconstitution inflammatory syndrome, CMV IRU. We found instead that T-regs in CMV IRU patients are functionally intact, while virus-specific immune responses and Th17 cells are compromised

Background. The immune reconstitution inflammatory syndromes (IRIS) are a spectrum of inflammatory conditions associated with opportunistic infections and occurring in ∼16% of human immunodeficiency type 1 (HIV-1)–infected patients given antiretroviral therapy. It has been proposed that these conditions are linked by a dysregulated immune system that is prone to exaggerated responses. However, immunologic studies have been limited by the availability of longitudinal samples from patients with IRIS and appropriate matched control subjects. Cytomegalovirus (CMV) immune recovery uveitis (IRU) is an IRIS occurring in up to 38% of patients with CMV retinitis. Although the pathologic immune responses occur in the eye, immune dysregulation that allows for development of pathologic responses is presumably caused by faulty systemic immune cell reconstitution.

Methods. We examined CMV-specific T cell responses, regulatory T (T_reg) cell function and polyclonal T cell responses, including IL-17 production, in 25 patients with CMV IRU and 49 immunorestored control subjects with CMV retinitis who did not develop IRU.

Results. Patients with CMV IRU had poor CMV-specific CD4⁺ T cell responses, as compared with control subjects, whereas CD8⁺ T cell responses were comparable. Patients with CMV IRU were characterized by smaller numbers of circulating Th17 cells. Deficiency in anti-CMV responses was not associated with differences in T_reg cell function.

Conclusions. The T_reg cell compartment is intact in patients with CMV IRU, and these patients do not develop exaggerated systemic CMV-specific or polyclonal immune responses. Cases are instead characterized by more profound depletion of Th17 cells and poor antiviral immune responses. CMV IRU may be most likely to develop in persons experiencing the greatest degree of immune dysfunction before initiating highly active antiretroviral therapy.