Objectives Investigate the feasibility of saliva sampling as a noninvasive and safer tool to detect SARS-CoV-2 and to compare its reproducibility and sensitivity with nasopharyngeal swab samples (NPS). The use of sample pools was also investigated. Methods 2107 paired samples were collected from asymptomatic health care and office workers in Mexico City. Sixty of these samples were also analyzed in two other independent laboratories for concordance analysis. Sample processing and analysis of virus genetic material were performed according to standard protocols described elsewhere. Pooling analysis was performed by analyzing the saliva pool and the individual pool components. Results The concordance between NPS and saliva results was 95.2% (Kappa: 0.727, p = 0.0001) and 97.9% without considering inconclusive results (Kappa: 0.852, p = 0.0001). Saliva had a lower number of inconclusive results than NPS (0.9% vs 1.9%). Furthermore, saliva shows a significantly higher concentration of both total RNA and viral copies than NPS. Comparison of our results with those of the other two laboratories shows 100% and 97% concordance. Saliva samples are stable without the use of any preservative, a positive SARS-CoV-2 sample can be detected 5, 10, and 15 days after collection when the sample is stored at 4 °C. Conclusions Our results indicate that saliva is as effective as NPS for the identification of SARS-CoV-2-infected asymptomatic patients, sample pooling facilitates the analysis of a larger number of samples with the benefit of cost reduction.

Acute Toxoplasma gondii infection comprises an immunosuppression stage, characterized by a reduction in T-cell proliferation in vitro. Treg cells maintain the homeostasis of the immune system, but their role in T. gondii-induced suppression has not been addressed. We show herein that immunosuppression, affecting both CD4 1 and CD8 1 T-cell proliferation, concurs with a reduction in Treg-cell number. The residual Treg cells, however, are activated and display an increased suppressive capacity. We show that selective elimination of Treg cells using Foxp3 EGFP mice leads to a full recovery of CD4 1 and CD8 1 T-cell proliferation. After Treg-cell removal, a reduced production of IL-10 was observed, but IL-2 levels were unchanged. The numbers of IL-10-producing Treg cells also increased during infection, although the in vitro neutralization of this cytokine did not modify T-cell proliferation, suggesting that IL-10 does not mediate the Treg-mediated suppression. However, addition of rIL-2 in vitro fully restored T-cell proliferation from infected animals. Thus, we show that Treg cells mediate the T-cell suppression observed during acute T. gondii infection through an IL-2-dependent mechanism. Our results provide novel insights into the regulation of the immune response against T. gondii.

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Regulatory T cells (Tregs) are CD4+Foxp3+ cells that modulate autoimmune responses. Tregs have been shown to be also involved during the immune response against infectious agents. The aim of this work is to study the role of Tregs during the infection with the intracellular protozoan Toxoplasma gondii. Resistant BALB/c mice were injected with 200 μg of anti-CD25 mAb (clone PC61) and 2 days later they were infected with 20 cysts of the ME49 strain of T. gondii. We observed that depleted mice showed 50–60% mortality during the acute infection. When FACS analysis was carried out, we observed that although injection of PC61 mAb eliminated 50% of Tregs, infected-depleted mice showed a similar percentage of CD25+Foxp3− (activated T cells, Tact) to those observed in infected nondepleted animals, demonstrating that in our depletion/infection system, injection of PC61 mAb did not hamper T cell activation while percentage of Tregs was reduced by 75% 10 days post infection. We concluded that Tregs are essential during protection in the acute phase of T. gondii infection.

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