# Complement-mediated and direct activation of human neutrophils induced by Premolis semirufa caterpillar toxins

## TL;DR

A caterpillar toxin causes inflammation by directly activating neutrophils and through the complement system, which could lead to joint damage.

## Contribution

The study identifies two distinct mechanisms of neutrophil activation by Premolis semirufa toxins and shows how complement inhibition reduces inflammation.

## Key findings

- Pararama hair extract directly activates neutrophils, increasing pro-inflammatory mediator release and degranulation.
- Complement activation in plasma from extract-treated blood further enhances neutrophil activation, which is reduced by compstatin and PMX205.
- Blocking complement components C3 and C5aR1 significantly attenuates inflammatory and degenerative effects of the extract.

## Abstract

Pararamosis is an occupational inflammatory disease caused by contact with hairs of the caterpillar Premolis semirufa, endemic to the Brazilian Amazon and primarily affecting rubber tree workers. Exposure to pararama hairs induces acute pruritic dermatitis and, in some cases, chronic joint inflammation resembling rheumatoid arthritis and osteoarthritis. Previous studies demonstrated that pararama hair extract activates the complement system and induces a robust inflammatory response in mouse models, characterized by cytokine production and immune cell recruitment. Given the critical role of neutrophils in inflammation and their activation by complement components, this study investigated the effects of pararama hair extract on human peripheral blood neutrophils.

Neutrophils isolated from healthy donors were directly stimulated with the extract or incubated with plasma derived from whole blood treated with the extract, in the presence or absence of compstatin, a C3 inhibitor that blocks complement activation, and PMX205, a selective C5aR1 antagonist applied directly to neutrophils. We assessed neutrophil activation by measuring cytokine and chemokine secretion, myeloperoxidase and elastase release, and neutrophil extracellular trap (NET) formation.

Our results reveal that pararama hair extract directly activates neutrophils, enhancing pro-inflammatory mediator release and degranulation. Moreover, plasma from extract-treated human whole blood samples further potentiated neutrophil activation, which was significantly reduced by compstatin, through inhibition of C3, and by selective blockade of the C5a receptor (C5aR1).

These findings highlight the integrated role of complement in neutrophil activation, as compstatin broadly inhibited complement-dependent effects, while PMX205 demonstrated the specific contribution of the C5a–C5aR1 axis. Targeting complement thus emerges as a promising strategy to mitigate inflammation and tissue damage in affected individuals.

Illustrating two mechanisms of neutrophil activation by the hair extract of the Premolis semirufa caterpillar (Pararama): a direct effect of the extract on neutrophils, and an indirect effect mediated by plasma derived from extract-treated whole blood, through complement activation. On the left, the extract directly induces the production of inflammatory mediators (IL-8, TNF-α, elastase, MPO) and the formation of NETs. On the right, the extract, when incubated with whole blood, activates the complement system, leading to the generation of C3a, C5a, and sTCC. Plasma derived from this activation stimulates neutrophils to produce IL-8, IL-6, TNF-α, elastase, and MPO. The action of complement inhibitors is represented by blue inhibitory lines: compstatin (C3 inhibitor), which prevents complement activation and thereby the generation of C3a, C5a, and sTCC; and PMX205 (C5aR1 antagonist), which blocks C5a–C5aR1 signaling on neutrophils. Both interventions reduce neutrophil outputs (IL-8, IL-6, TNF-α, elastase, MPO). In both contexts, activated neutrophils contribute to inflammation, cellular infiltration, oxidative stress, matrix degradation, cartilage erosion, and joint damage. Moreover, inhibition by compstatin and PMX205 attenuates these inflammatory and degenerative effects. Red arrows indicate inflammatory outcomes, whereas blue inhibitory lines represent inhibitory/anti-inflammatory actions. Created with BioRender.com.Illustration showing the effects of Pararama hair extract, with a caterpillar at the top. The left side depicts direct action causing inflammation and related processes. The right side describes plasma treatment, highlighting complement system activation and subsequent inflammatory responses, leading to joint damage. Key molecules include Compstatin, C3a, and C5a.

Illustrating two mechanisms of neutrophil activation by the hair extract of the Premolis semirufa caterpillar (Pararama): a direct effect of the extract on neutrophils, and an indirect effect mediated by plasma derived from extract-treated whole blood, through complement activation. On the left, the extract directly induces the production of inflammatory mediators (IL-8, TNF-α, elastase, MPO) and the formation of NETs. On the right, the extract, when incubated with whole blood, activates the complement system, leading to the generation of C3a, C5a, and sTCC. Plasma derived from this activation stimulates neutrophils to produce IL-8, IL-6, TNF-α, elastase, and MPO. The action of complement inhibitors is represented by blue inhibitory lines: compstatin (C3 inhibitor), which prevents complement activation and thereby the generation of C3a, C5a, and sTCC; and PMX205 (C5aR1 antagonist), which blocks C5a–C5aR1 signaling on neutrophils. Both interventions reduce neutrophil outputs (IL-8, IL-6, TNF-α, elastase, MPO). In both contexts, activated neutrophils contribute to inflammation, cellular infiltration, oxidative stress, matrix degradation, cartilage erosion, and joint damage. Moreover, inhibition by compstatin and PMX205 attenuates these inflammatory and degenerative effects. Red arrows indicate inflammatory outcomes, whereas blue inhibitory lines represent inhibitory/anti-inflammatory actions. Created with BioRender.com.