Acanthamoeba spp. are free-living amoebae (FLA) found worldwide in diverse ecological environments, including soil, air, sewage, seawater, tap and bottled water, air, dust, sewage samples, and plant surfaces (Schuster et al., 2004; Visvesvara et al., 2007). Acanthamoeba spp. can cause opportunistic infections, such as granulomatous amoebic encephalitis (GAE), nasopharyngeal infections, cutaneous acanthamoebiasis (CA) and systemic infections in immunocompromised patients, or non-opportunistic infections such as Acanthamoeba keratitis (AK) in otherwise healthy people (Reddy et al., 2022).

Skin lesions occur in 90 % of patients with disseminated acanthamoebiasis, especially in patients with GAE (Galarza et al., 2009; Paltiel et al., 2004). CA is increasingly found, especially in immunocompromised patients. CA has been described in HIV-infected and solid organ transplant (SOT) patients (Paltiel et al., 2004). The important risk factors of Acanthamoeba skin lesions include surgical scars, bites and mechanical trauma and viral lesions (Galarza et al., 2009; Król-Turmińska and Olender, 2017). Acanthamoeba spp. skin infections may originate in skin wounds and subsequently spread to various organs, or they may begin in different organs and then manifest in the skin (Hernández-Jasso et al., 2020). In patients with CA, a single or disseminated chronic skin lesions, which are most commonly crusted or ulcerated, can be observed. These lesions may appear as reddish nodules, skin ulcers, or abscesses in the skin. The skin lesions exhibit an intact epidermis with suppurative inflammation of the subcutis (Tan et al., 1993). CA carries a mortality rate of over 70 %, predominantly occurring in immunosuppressed patients (Park et al., 2023).

The skin is the first line of defense against pathogens. In the case of skin injury, the initiation of an inflammatory response is critical for proper healing (Borkowski et al., 2013). In cutaneous parasitic infections, multiple factors such as skin microbiota, host immune response, lesion location and the species have an influence on the outcome of parasitosis (Saidi et al., 2023). Pathogens penetrate the skin and activate the innate immune system, which can lead to the development of adaptive reactions (Tamagawa-Mineoka, 2023).

One of the best-studied families of pattern recognition receptors is toll-like receptors (TLRs) that identify specific microbial products (Barton and Kagan, 2009). However, TLRs may also recognize self-epitopes that are released from damaged cells or are present at the surface of apoptotic cells (Marshak-Rothstein and Rifkin, 2007; Leadbetter et al., 2002). The subsequent release of non-coding double-stranded RNA from necrotic keratinocytes has been identified as an endogenous activator of toll-like receptor 3, TLR3 (Borkowski et al., 2013). TLR3 may have multiple functions in the skin and may signal the start of barrier repair processes. TLR3 activation increased expression of genes critical to barrier formation and the epithelial barrier repair response (Borkowski et al., 2013). Additionally, recent research demonstrated that TLR3 is important for wound healing, as Tlr3−/− mice have a slightly delayed wound healing phenotype (Lin et al., 2011). It was also reported that enhanced TLR3 expression and function in keratinocytes may be caused by interferon γ, IFN-γ (Kajita et al., 2015). IFN-γ is a representative Th1 cytokine, and it is involved in cutaneous immune responses such as contact hypersensitivity reactions (Mori et al., 2008). Additionally, IFN-γ plays a significant role in protecting keratinocytes from viruses and bacteria as well as controlling some parasitic infections (Banno et al., 2003; Brauweiler et al., 2016; Kima and Soong, 2013).

Another TLR that plays an important role in the skin is TLR7. It was found that TLR7 defines keratinocytes that possess the fundamental characteristics of interfollicular epidermal stem cells (Yin et al., 2014). Additionally, the TLR7 ligand is often used to treat primary skin tumors, cutaneous metastases, cutaneous warts and actinic keratoses (Ermertcan et al., 2011; Hari et al., 2010). Both TLR7 and TLR3 are involved in expression of interleukin 23, IL-23 (Al-Salleeh et al., 2007). Recent clinical trials have shown that monoclonal antibodies against IL-23 are effective in the treatment of patients with skin diseases (Chan et al., 2018; Liu et al., 2020).

Therefore, the aim of the study was to examine the gene and protein expression of TLR3, TLR7, IFN-γ, and IL-23 in the skin of mice with disseminated acanthamoebiasis.