Cryptococcosis-IRIS is associated with lower cryptococcus-specific IFN-γ responses before antiretroviral therapy but not higher T-cell responses during therapy.

Cryptococcal meningitis (CM) is the leading cause of adult meningitis in southern and central Africa and it particularly affects persons infected with human immunodeficiency virus (HIV), accounting for 13%–44% of HIV-related deaths [1]. Morbidity and mortality associated with this condition are affected by cryptococcosis-associated immune reconstitution inflammatory syndrome (C-IRIS), which has been reported in up to 50% of HIV-infected patients with treated CM who commence combination antiretroviral therapy (cART) [2]. Like tuberculosis-IRIS, the immunopathogenesis of C-IRIS is poorly understood; both are thought to be due, in part, to an aberrant interferon-gamma (IFN-γ) driven Th1 response to pathogen-specific antigens [3]. A better understanding of C-IRIS pathogenesis is necessary to recognize high-risk patients and develop diagnostic and treatment strategies. Currently, the diagnosis of C-IRIS remains a diagnosis of exclusion [4]. No definitive diagnostic marker or predictive signature has been adopted into clinical practice, outside of research settings [5]. Distinguishing C-IRIS from other causes of neurological deterioration (ND) after commencing cART is crucial as management and prognosis are vastly different. Analysis of T-cell responses to cryptococcal antigens may be informative. Whole blood assays for detecting pathogen-specific T cells bear potential as a “field-based assay” that would be particularly attractive in resource-limited settings. Readouts may include expression of activation markers on CD4+ T cells and production of cytokines and chemokines by antigen-activated T cells and other cells activated by these T cells. Accordingly, coexpression of CD25 (interleukin-2 receptor-alpha chain) and CD134 (OX40) on CD4+ T cells in whole blood incubated with antigens has been suggested as an alternative measure of activated and proliferating antigen-specific memory CD4+ T cells [6, 7]. Cryptococcal mannoproteins (CMP) are a group of heterogenous T-cell antigenic determinants isolated from Cryptococcus neoformans [8]. CMPs stimulate lymphoproliferative responses and cytokine production in patients recovering from cryptococcosis [9, 10] and have been shown experimentally to induce the production of tumor necrosis factor-alpha, IL-12, and IFN-γ in human peripheral blood monouclear cells (PBMCs) and murine macrophages cocultured with T cells [8, 11–13]. We explored the use of a whole blood assay to detect CMP-reactive T cells that expressed CD25 and CD134 or produced IFN-γ as a potential field-based assay for the prediction and diagnosis of paradoxical central nervous system (CNS) C-IRIS. CXCL10 (also known as IFN-γ–inducible protein 10 [IP-10]) and IL-10 were also assayed in plasma from the whole blood cultures as the former is induced by IFN-γ and the latter is an antiinflammatory and regulatory cytokine.