Scabies is a neglected tropical disease and represents a considerable global burden. Although consensus diagnostic criteria for scabies have been recently published, diagnosing scabies infestation remains challenging in clinical practice. We investigated the diagnostic utility of complete blood cell count (CBC) and CBC-derived ratios obtained at diagnosis in a set of 167 patients who are Vietnamese with confirmed scabies. These parameters were compared with those of patients with dermatophytosis (N = 800) and urticaria (N = 2023), two diseases frequent in Vietnam, which can present with similar skin manifestations to scabies and tend to pose a diagnostic challenge in vulnerable populations. Our analysis revealed that white blood cell, monocyte, and eosinophil counts were significantly higher among patients with scabies than the other two diseases. Similarly, the monocyte-to-lymphocyte ratio (MLR) and eosinophil-to-lymphocyte ratio (ELR) were significantly higher among patients with scabies. The optimal cut-off values to distinguish scabies from dermatophytosis and urticaria were 0.094 for ELR (sensitivity: 74.85%, specificity: 70.7%) and 0.295 for MLR (sensitivity: 52.69%, specificity: 73.54%). CBC, ELR, and MLR are low-cost and easily calculated parameters that may be helpful for the diagnosis of scabies.

Mucosal-associated invariant T cells (MAIT cells) are a subset of T cells with innate, effector-like properties that play an essential role in the immune response to microbial infections. In humans, MAIT cells are detectable in the blood, liver, and lungs, but little is known about the frequency of these cells in the bone marrow. Also, the pathogenic role, if any, of MAIT cells in the development of aplastic anemia, a disease with an exquisite origin in the bone marrow, is currently unknown. We investigated the frequency and clinical relevance of bone marrow MAIT cells in a cohort of 14 patients (60.6 ± 23 and 57% women) with aplastic anemia. MAIT cells in the bone marrow samples obtained at diagnosis were evaluated by flow cytometry, and their association with various blood cell parameters and the patients’ clinical features was analyzed. MAIT cells were detectable in the bone marrow of all patients, with considerable variations among them. Bone marrow MAIT cells expressing the activator receptor natural killer group 2D - NKG2D (NKG2D+ MAIT cells) were significantly more abundant in the specimens of the aplastic anemia patients than in patients with bone marrow failure distinct from aplastic anemia. In addition, the NKG2D+ MAIT cells positively correlated with whole blood cell counts (WBC), platelet counts, and neutrophil counts, as well as with various inflammatory markers, including neutrophil-to-lymphocyte rate (NLR), platelet-to-lymphocyte rate (PLR), and systemic inflammatory index (SII). In functional studies, bone marrow CD34+ hematopoietic cells exposed to phytohemagglutinin or bacterial-derived lipopolysaccharide and acetyl-6-formylpterin upregulated MR1 (major histocompatibility complex, class I-related, known to interact with MAIT cells) and MICA/B (MHC class I chain-related gene A, a ligand of NKG2D) proteins on their cell surface, suggesting that under stress conditions, CD34+ hematopoietic cells are more likely to interact with NKG2D+ MAIT cells. In addition, NKG2D+ MAIT cells upregulated perforin and granzyme B in response to their interaction with recombinant MICA protein in vitro. This study reports for the first time the frequency of MAIT cells in the bone marrow of patients with aplastic anemia and assesses the potential implications of these cells in the pathogenesis or progression of aplastic anemia.