a = Missing clinical data due to leaving against medical advice. Missing CSF due to being processed at external laboratories with incomplete diagnostic analysis and without CSF storage.
b = 13 specimens had inadequate volume for CSF storage and did not have cytokine profiling performed.
c = one person had both relapse and IRIS
d = 27 CM-IRIS CSF specimens were stored.

The human immune response to Cryptococcus neoformans depends on coordinated interaction of antigen presenting cells with a type-1 CD4 T-helper (Th₁) cell response. A. The immune response begins with innate defense in the submucosa through alternative complement opsonization of C. neoformans which allows for efficient phagocytosis by neutrophils, macrophages, and dendritic cells [17–20]. B. Dendritic cells localize the pathogen to the endolysosome through phagocytosis where the organism is degraded, processed, and antigenic peptides presented on surface major histocompatibility complex class-II (MHC-II) to T-cells in lymphatic tissue [20, 21]. C&D. When T-cells have a matching T-cell receptor for the peptide, appropriate cytokine signals from dendritic cells allow naïve Th₀ T-cells to differentiate into effector T-cells [22]. E. These effector T-cells, are important in the classical activation of macrophages via interferon-gamma (IFN-γ) for fungal clearance. VEGF is secreted by CD4 T-cells after mannoprotein antigen recognition via MHC class II by macrophages resulting in increases in vascular permeability, chemotaxis of additional macrophages and CD4+CD45RO+ memory T-cells. Macrophages require IFN-γ stimulation to up-regulate anti-microbial peptides, reactive oxygen species, and pro-inflammatory cytokines such as interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α), thereby sufficiently killing the phagocytosed, facultative intracellular fungal cells [22]. In the absence of an effective Th₁ T-cell response, humoral immunity via IgG1, IgG2a, and IgG2b directed toward GXM is ineffective alone [23, 24], and the adaptive arm of the immune system remains paramount to cryptococcal defense. Observation of delayed-type hypersensitivity responses, requirements for cell-mediated immunity, and IFN-γ dependence all support that a Th₁ response is essential to cryptococcal immunity [22, 25, 26]. In human clinical studies, the IFN-γ (Th₁ cytokine) present in the CSF is associated with the rate of fungal culture clearance [29, 37, 38].

Figure 3 displays the initial CSF profile (only) in ART-naïve persons with a first episode of cryptococcal meningitis compared to their later risk of cryptococcal-related IRIS with CNS manifestations after initiating HIV therapy. Persons with “Future IRIS” after starting HIV therapy had less initial inflammation in their CSF compared to persons with uneventful immune reconstitution with ART (“No IRIS”). The pattern of inflammation is consistent with a decreased Th₁ response in persons with future IRIS. Th₁ immune responses are necessary for cryptococcal clearance, thus persons with a highly dysfunctional immune system may be predisposed to IRIS by failing to effectively clear antigen, even though they have similar CD4 counts and similar burden of initial CM infection at time of initial cryptococcal meningitis (e.g. similar CRAG titer and quantitative culture). The Y-axis units for white blood cells (WBC) are cells/μL; protein is mg/dL; cytokines and chemokines are pg/mL. Other CSF cytokines with low levels, but statistically different levels were: IL-4 (median 1.4 pg/mL overall; P=.047) and IL-1β (median 2.3 pg/mL overall; P=.035).
Abbreviations: IL=interleukin; G-GSF = granulocyte colony stimulating factor; IFN-γ = interferon-gamma; TNF-α = tumor necrosis factor–alpha; CRAG = cryptococcal antigen