A key unsolved question in the current coronavirus disease 2019 (COVID-19) pandemic is the duration of acquired immunity. Insights from infections with the four seasonal human coronaviruses might reveal common characteristics applicable to all human coronaviruses. We monitored healthy individuals for more than 35 years and determined that reinfection with the same seasonal coronavirus occurred frequently at 12 months after infection. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel coronavirus responsible for an ongoing pandemic. To date, there is limited evidence of reinfection by SARS-CoV-2, although it is generally assumed that reinfections by coronaviruses occur. To prepare for future waves of Coronavirus Disease 2019 (COVID-19), it is important to elucidate the duration of protection to reinfection for which the seasonal coronaviruses might serve as an informative model. There are four species of seasonal coronaviruses-HCoV-NL63, HCoV-229E, HCoV-OC43 and HCoV-HKU1-that all can cause respiratory tract infections but

Chimpanzees are susceptible to infection by di- No antibodies to the carboxyl terminus of HTLV-IUB gpl20 were observed in sera of chimpanzees inoculated with HTLV-ITIRF or with the brain-tissue strain, and those sera did not neutralize HTLV-IIIB. A rabbit immunized with the C-terminal portion of gpl20 acquired neutralizing antibodies that bound to four domains of the HTLV-UIB external envelope as analyzed by reactivity to 536 overlapping nonapeptides of gpl20. One of these domains in the variable region V3, with the amino acid sequence IRIQRGPGRAFVTIG (amino acids 307-321), bound to all chimpanzee sera that neutralized HTLV-IIIB but not to the serum of the HTLV-IUIRF-inoculated chimpanzee that did not neutralize HTLV-UIB. The HTLV-IIIRF sequence at the same location, ITKGPGRVIYA, was recognized by the serum of the HTLV-UIERF-inoculated chimpanzee but not by any sera of the HTLV-IUB-inoculated or LAV-i-inoculated chimpanzees. The HTLV-UIB residues RIQR and AFV and the HTLV-IIRF residues lysine and VIYA, flanking a highly conserved (3-turn (GPGR), appear to be critical for antibody binding and subsequent type-specific virus neutralization. This neutralization epitope, putatively consisting of a loop between two cysteine residues (amino acids 296 and 331) connected by a disulfide bond, is immunodominant in HIV-1-infected chimpanzees and induces antibodies restricted to the homologous viral strain.

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