According to the study, researchers examined the mechanisms of skin inflammation produced by different pathogens. The clinical presentations of skin diseases produced by different pathogens, as American tegumentary leishmaniasis (ATL) and sporotrichosis can be similar and possibly influenced by the skin immune system (SIS).

They used immunohistochemistry to analyze 96 patients: a- localized cutaneous leishmaniasis (LCL-ATL); b- sporotrichoid cutaneous leishmaniasis (SCL-ATL); c-lymphocutaneous (LC-SP); d- fixed (F-SP) sporotrichosis. LCL-ATL and SCL-ATL had a significantly higher percentage of CD8, FasL and NOS2 than sporotrichosis. Immunologists have recently paid more attention to the importance of the skin for immune surveillance.

In humans, the skin, which covers approximately 2 m2 and accounts for 16% of the body weight, is the largest organ of the body. This organ has several immune systems, such as the skin immune system (SIS), skin-associated lymphoid tissue (SALT), and hair follicle immune system (HFIS).

In this study, we compared the in situ inflammatory response of ATL and SP, cutaneous lesions in order to evaluate how the skin immune system reacts to pathogens with different natures and in patients with diverse or similar clinical aspects. The results have pointed to a general and similar inflammatory skin reaction with some differences according to the infection/clinical presentation.

Although both infections primarily target the skin, they can present different degrees of in situ granulomatous reactions and different courses of disease. SP is often a subacute infection, which is characterized by an exudative reaction, whereas ATL is a chronic disease, which is characterized by a long duration of infection and the presence of non-exudative ulcers.

They observed differences in the clinical presentation of ATL and SP. For example, ATL lesions developed more slowly than the SP lesions. In fact, after only 2 weeks of infection, 6 SP patients had already developed lesions. These observations suggest a relationship between the nature of the etiological agent and the immune response leading to the development of acute, subacute, or chronic lesions.

In addition, they cannot exclude the possibility that, during infection, Leishmania amastigotes and Sporothrix spp yeasts can be transiently localized in the extracellular and intracellular milieu, respectively.

Authors conclude that, the SIS is a complex, adaptable structure that is capable of responding with plasticity to intracellular or extracellular pathogens in order to control microorganism burden.

In the clinical presentation of infectious skin diseases could result from a combination of factors from both, the host SIS and the etiological agent. Since more severe lesions from both SP and ATL presented an important concentration of neutrophils, or CD8+ T cells and NOS2 expression, respectively, our results also suggest that, unbalanced host SIS – parasite relationship can lead to more severe manifestations of skin infectious diseases.