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Public health authorities have been paramount in guaranteeing that adequate fresh air ventilation is promoted in classrooms to avoid SARS-CoV-2 transmission in educational environments. In this work it was aimed to assess ventilation conditions (carbon dioxide, CO 2 ) and suspended particulate matter (PM 2.5 , PM 10 and UFP) levels in 19 classrooms – including preschool, primary and secondary education – located in the metropolitan area of Ciudad Real, Central-Southern Spain, during the school’ reopening (from September 30th until October 27th, 2020) after about 7 months of lockdown due to COVID-19 pandemic. The classrooms that presented the worst indoor environmental conditions, according to the highest peak of concentration obtained, were particularly explored to identify the possible influencing factors and respective opportunities for improvement. Briefly, findings suggested that although ventilation promoted through opening windows and doors according to official recommendations is guaranteeing adequate ventilation conditions in most of the studied classrooms, thus minimizing the risk of SARS-CoV-2 airborne transmission, a total of 5 (26%) surveyed classrooms were found to exceed the recommended CO 2 concentration limit value (700 ppm). In general, preschool rooms were the educational environments that registered better ventilation conditions, while secondary classrooms exhibited the highest peak and average CO 2 concentrations. In turn, for PM 2.5 , PM 10 and UFP, the concentrations assessed in preschools were, on average about 2-fold greater than the levels obtained in both primary and secondary classrooms. In fact, the indoor PM 2.5 and PM 10 concentrations substantially exceeded the recommended limits of 8hr-exposure, established by WHO, in 63% and 32% of the surveyed classrooms, respectively. Overall, it is expected that the findings presented in this study will assist the establishment of evidence-based measures (mainly based on ensuring proper ventilation rates and air filtration) to mitigate preventable environmental harm in public school buildings, mainly at local and national levels.

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An antigen-binding radioimmunoassay was used to measure IgG, IgA and IgE antibody (ab) to Dermatophagoides pteronyssinus in sera from patients who had been hyposensitized with either aqueous D. pteronyssinus extract or placebo. An allergen, F₄P₁, was obtained from D. pteronyssinus culture and ¹²⁵I-labelled for use in the assay. The radio-allergosorbent test was also used to measure IgE ab to D. pteronyssinus and IgE ab to Dermatophagoides farinae. The radioimmunoassay results showed a selective rise in IgG ab in sera from D. pteronyssinus-treated (DP) patients. An increase of greater than twofold in IgG ab in post-treatment sera was found in 27 of 29 DP patients compared to 1 of 29 placebo-treated (‘placebo’) patients (p < < 0.001). The mean rise in IgG ab in DP patients was sixfold, and the maximum rise was 50-fold. There was little change in the levels of IgA ab or IgE ab in either DP or ‘placebo’ patients during treatment. The DP patients showed significant clinical improvement compared with the ‘placebo’ patients (p < 0.01). However, no correlation was found between post-treatment IgG ab and post-treatment symptom scores, or between the changes in IgG ab and the changes in symptom scores during treatment. The time course of the antigen-binding assay was investigated using very low concentrations of F₄P₁ The results showed that antigen-binding was slow, even in the presence of an excess of IgG ab. The role of IgG ab in hyposensitization is discussed.

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