Mpina, M. | bioRxiv Science

bioRxiv2024

Granulysin antimicrobial activity promotes dormancy in Mycobacterium tuberculosis

Human tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) remains a global public health threat. Granulomas constitute a hallmark of TB pathogenesis that can clear, contain or exacerbate an infection. Containment is exploited by Mtb as a hideout to persist in a dormant, antibiotic-tolerant state only to resuscitate upon immunosuppression. The immune determinants of a granulomatous response driving Mtb persistence remain elusive. We here combined an ex vivo granuloma model with peripheral blood mononuclear cell (PBMC) specimens from TB patients and a high-dimensional mass cytometry (CyTOF) approach to shed light on the immune factors prompting Mtb dormancy. Compared to healthy controls, patient-derived ex vivo granulomas rapidly force Mtb to adopt a dormant-like state; an observation that correlates with the presence of activated innate (-like) cytotoxic lymphocytes. We further demonstrate that Mtb dormancy is induced by direct exposure to granulysin, thereby unravelling an immune escape mechanism to cytotoxic lymphocyte activity.

immunology↗

bioRxiv2021

Analysis of nucleic acids extracted from rapid diagnostic tests reveals a significant proportion of false positive test results associated with recent malaria treatment

Surveillance programs often use malaria rapid diagnostic tests (RDTs) to determine the proportion of the population carrying parasites in their peripheral blood to assess the malaria transmission intensity. Despite an increasing number of reports on false-negative and false-positive RDT results, there is a lack of systematic quality control activities for RDTs deployed in malaria surveillance programs. Our study provides a larger scale comparative evaluation of RDTs used in the 2018 Malaria Indicator Survey (MIS) conducted on Bioko Island, Equatorial Guinea. We conducted a molecular analysis by extraction of nucleic acids from 1,800 negative and 1,065 positive RDTs followed by qPCR analysis. These results were combined with a dataset collected in a comprehensive questionnaire from each MIS participant. Of the 2,865 RDTs that were collected in 2018 on Bioko Island and analysed in our study, 4.7% had a false-negative result. These false-negative RDT results were associated with low parasite density infections. In a substantial proportion of samples, we identified masked pfhrp2 and pfhrp3 gene deletions in which at least one P. falciparum strain carried a gene deletion. Among all positive RDTs analysed, 28.4% were tested negative by qPCR and therefore considered to be false-positive. Analysing the questionnaire data collected from the participants, this high proportion of false-positive RDT results could be explained by PfHRP2 antigen persistence after recent malaria treatment. We conclude that malaria surveillance depending solely on RDTs needs well-integrated quality control procedures assessing the extend and impact of reduced sensitivity and specificity of RDTs on malaria control programs.

microbiology↗