Exploring the complex role of IL-32γ in American Tegumentary Leishmaniasis - a cytokine that both controls infection and drives tissue destruction.
Imagine a microscopic battle raging within skin cells, where the very defenses meant to protect the body instead cause devastating damage. This is the paradox facing patients with American Tegumentary Leishmaniasis, a parasitic disease that affects thousands each year. At the heart of this conflict lies a mysterious immune molecule—Interleukin 32 gamma (IL-32γ)—that plays a contradictory role in both controlling infection and driving tissue destruction 1 .
Recent research has begun to unravel this molecular mystery, revealing a complex relationship between IL-32γ and other key immune players that determines whether patients experience simple skin ulcers or disfiguring mucosal damage 1 2 .
IL-32γ demonstrates a dual nature in leishmaniasis: it helps control the parasite but also contributes to the tissue damage that characterizes the disease.
Interleukin-32 is no ordinary immune signaling molecule. Discovered in 2005 and originally called NK4, IL-32 doesn't resemble any known cytokine family 4 . This orphan cytokine exists in nine different forms (isoforms) created through alternative splicing of its genetic code, with IL-32γ standing out as the most biologically potent variant 5 .
IL-32γ demonstrates remarkable versatility in the immune landscape. It can stimulate the vitamin D-dependent microbicidal pathway, increasing production of antimicrobial peptides 5 .
American Tegumentary Leishmaniasis (ATL) represents a spectrum of diseases caused by protozoan parasites of the Leishmania genus, predominantly L. braziliensis in South America 1 8 . The condition manifests in two primary forms:
Characterized by single or multiple skin ulcers that may heal spontaneously but often leave scars.
A more severe form where the parasite invades nasal or oral mucosa, causing progressive tissue destruction that never heals without treatment 1 .
While a robust immune response is necessary to control the parasite, an overly exuberant reaction causes significant collateral damage to tissues. The balance between these opposing forces—parasite control versus tissue preservation—determines disease outcome and severity.
A groundbreaking 2014 study set out to investigate whether IL-32 played a role in American Tegumentary Leishmaniasis, marking the first time this cytokine had been studied in protozoan infections 1 .
The study included 24 cutaneous leishmaniasis patients, 10 mucosal leishmaniasis patients, and appropriate controls with healthy skin (n=8) and mucosa (n=7) 1 .
Protein expression of IL-32, TNF, and IL-10 was evaluated in lesions using immunohistochemistry, allowing researchers to visualize exactly where these cytokines were produced within tissues 1 .
The researchers used quantitative PCR to measure different IL-32 isoforms (α, β, δ, γ) in tissue biopsies, along with TNF and IL-10 mRNA 1 .
Peripheral blood mononuclear cells (PBMCs) from healthy donors were exposed to L. (V.) braziliensis amastigotes to observe direct effects on IL-32 expression 1 .
| Tissue Type | IL-32γ mRNA Expression | IL-32 Protein Production | Primary Cell Sources |
|---|---|---|---|
| Cutaneous Lesions (CL) | Significantly Upregulated | Detected in lesions | Epithelial, endothelial, mononuclear cells, giant cells |
| Mucosal Lesions (ML) | Significantly Upregulated | Detected in lesions | Epithelial, endothelial, mononuclear cells, giant cells |
| Healthy Skin | Low/Baseline | Minimal | Rare/Negligible |
| Healthy Mucosa | Low/Baseline | Minimal | Rare/Negligible |
The findings revealed that IL-32γ was the predominant isoform expressed in both cutaneous and mucosal lesions, with similar upregulation in both clinical forms 1 .
| Cytokine Pair | Association in Cutaneous Leishmaniasis | Association in Mucosal Leishmaniasis | Interpretation |
|---|---|---|---|
| IL-32 & TNF | No significant association | Strong positive correlation | TNF association specific to mucosal form |
| IL-32 & IL-10 | No association | No association | Not linked to anti-inflammatory pathway |
| TNF & IL-10 | Independent expression | Independent expression | No direct counter-regulation observed |
Perhaps the most intriguing finding was the differential relationship between IL-32 and TNF in the two clinical forms. While IL-32 protein expression was associated with TNF in mucosal lesions, this connection was absent in cutaneous lesions 1 . This suggests distinct inflammatory pathways drive the different clinical manifestations.
Visual representation of IL-32γ mRNA expression levels across different tissue types based on experimental data.
Visualizes IL-32, TNF, and IL-10 protein distribution within tissue sections.
Measures and differentiates between various IL-32 isoform mRNA expression levels.
Isolated immune cells used for in vitro infection studies with Leishmania parasites.
Identifies and confirms Leishmania species and subgenera in patient samples.
Used to study direct effects of IL-32γ on various cell types and immune responses.
Blocks IL-32 function to investigate its specific role in anti-leishmanial immunity.
A 2025 study using advanced spatial transcriptomics identified IL-32-producing CD8+ memory T cells as key components of immunoregulatory niches in cutaneous leishmaniasis lesions across patient populations in Sri Lanka, Brazil, and India 2 .
Remarkably, the abundance of these IL-32+ cells at treatment initiation negatively correlated with cure rates, suggesting IL-32 might serve as a biomarker for treatment response 2 .
The genetic underpinnings of IL-32 responses have also come into focus. Different genetic variants of IL-32 may influence individual susceptibility to American Tegumentary Leishmaniasis, while specific isoforms appear associated with distinct T helper lymphocyte profiles 5 .
This genetic dimension helps explain why patients exhibit such varied responses to the same parasite.
Further illuminating the protective mechanisms, research reveals that IL-32γ is essential for the vitamin D-dependent microbicidal pathway that controls parasite replication 5 . This pathway involves IL-32γ-induced expression of an enzyme (CYP27B1) that converts inactive vitamin D to its bioactive form, which in turn triggers production of antimicrobial peptides like cathelicidin and β-defensin 5 .
The therapeutic implications of these findings are substantial. As one review noted, "the identification of parasite factors and host receptors responsible for IL-32γ production are important to the control of Leishmania and the development of new therapeutic strategies" 8 .
Understanding how to modulate IL-32 responses—enhancing its beneficial antimicrobial effects while limiting its tissue-damaging inflammation—could lead to more effective treatments for this neglected tropical disease.
The discovery of IL-32γ's elevated presence in cutaneous and mucosal leishmaniasis lesions and its association with TNF represents a significant advancement in understanding the immunopathology of this complex disease. IL-32γ emerges as a crucial player at the intersection of protective immunity and destructive inflammation—a true double-edged sword in the host-parasite battle.
As scientists continue to decode the mysteries of IL-32γ in leishmaniasis, they move closer to harnessing its power for patient benefit—potentially developing new diagnostic tools, prognostic biomarkers, and targeted therapies that can maintain its protective effects while minimizing collateral damage to tissues. In the ongoing battle against leishmaniasis, this orphan cytokine may yet find its place in the medical arsenal.