Seroprevalence as an Indicator of Undercounting of COVID-19 Cases in a Large Well-Described Cohort.

Introduction: Reported confirmed cases represent a small portion of overall true cases for many infectious diseases. The undercounting of true cases can be considerable when a significant portion of infected individuals are asymptomatic or minimally symptomatic, as is the case with COVID-19. Seroprevalence studies are an efficient way to assess the extent to which true cases are undercounted during a large-scale outbreak and can inform efforts to improve case identification and reporting. Methods: A longitudinal seroprevalence study of active duty U.S. military members was conducted from May 2020 through June 2021. A random selection of service member serum samples submitted to the Department of Defense Serum Repository was analyzed for the presence of antibodies reactive to SARS-CoV-2. The monthly seroprevalence rates were compared with those of cumulative confirmed cases reported during the study period. Results: Seroprevalence was 2.3% in May 2020 and increased to 74.0% by June 2021. The estimated true case count based on seroprevalence was 9.3 times greater than monthly reported cases at the beginning of the study period and fell to 1.7 by the end of the study. Conclusions: In our sample, confirmed case counts significantly underestimated true cases of COVID-19. The increased availability of testing over the study period and enhanced efforts to detect asymptomatic and minimally symptomatic cases likely contributed to the fall in the seroprevalence to reported case ratio.

Post-vaccination serum cytokines levels correlate with breakthrough influenza infections.

Post-vaccination cytokine levels from 256 young adults who subsequently suffered breakthrough influenza infections were compared with matched controls. Modulation within the immune system is important for eliciting a protective response, and the optimal response differs according to vaccine formulation and delivery. For both inactivated influenza vaccine (IIV) and live attenuated influenza vaccines (LAIV) lower levels of IL-8 were observed in post-vaccination sera. Post-vaccination antibody levels were higher and IFN-γ levels were lower in IIV sera compared to LAIV sera. Subjects who suffered breakthrough infections after IIV vaccination had higher levels of sCD25 compared to the control group. There were differences in LAIV post-vaccination interleukin levels for subjects who subsequently suffered breakthrough infections, but these differences were masked in subjects who received concomitant vaccines. Wide variances, sex-based differences and confounders such as concomitant vaccines thwart the establishment of specific cytokine responses as a correlate of protection, but our results provide real world evidence that the status of the immune system following vaccination is important for successful vaccination and subsequent protection against disease.

Establishment of SARS-CoV-2 genomic surveillance within the Military Health System during 1 March-31 December 2020.

This report describes SARS-CoV-2 genomic surveillance conducted by the Department of Defense (DoD) Global Emerging Infections Surveillance Branch and the Next-Generation Sequencing and Bioinformatics Consortium (NGSBC) in response to the COVID-19 pandemic. Samples and sequence data were from SARS-CoV-2 infections occurring among Military Health System (MHS) beneficiaries from 1 March to 31 December 2020. There were 1,366 MHS samples sequenced from 10 countries, 36 U.S states or territories, and 5 Geographic Combatant Commands, representing approximately 2% of DoD cases in 2020. Genomes from these samples were compared with other public sequences; observed trends were similar to those of Centers for Disease Control and Prevention national surveillance in the U.S. with B.1, B.1.2, and other sub-lineages comprising the dominant variants of SARS-CoV-2. Sequence data were used to monitor transmission dynamics on U.S. Navy ships and at military training centers and installations. As new variants emerge, DoD medical and public health practitioners should maximize the use of genomic surveillance resources within DoD to inform force health protection measures.

Borrelia burgdorferi intercepts host hormonal signals to regulate expression of outer surface protein A.

The Borrelia burgdorferi infectious cycle requires that the organism adapt to vast differences in environmental conditions found in its tick and mammalian hosts. Previous studies have shown that B. burgdorferi accomplishes this accommodation in part by regulating expression of its surface proteins. Outer surface protein A (OspA) is a borrelial protein important in colonization of the tick midgut. OspA is up-regulated when the organism is in its tick host and down-regulated when it is in a mammalian host. However, little is known about how it is up-regulated again in a mammalian host in preparation for entry into a feeding tick. Here, we report that the host neuroendocrine stress hormones, epinephrine and norepinephrine, are specifically bound by B. burgdorferi and result in increased expression of OspA. This recognition is specific and blocked by competitive inhibitors of human adrenergic receptors. To determine whether recognition of catecholamines, which are likely to be present at the site of a tick bite, may play a role in preparing the organism for reentry into a tick from a mammalian host, we administered a beta-adrenergic blocker, propranolol, to infected mice. Propranolol significantly reduced uptake of B. burgdorferi by feeding ticks and decreased expression of OspA in B. burgdorferi recovered from ticks that fed on propranolol-treated mice. Our studies suggest that B. burgdorferi may co-opt host neuroendocrine signals to inform the organism of local changes that predict the presence of its next host and allow it to prepare for transition to a new environment.

Pulmonary V beta 4+ T cells from Histoplasma capsulatum-infected mice respond to a homologue of Sec31 that confers a protective response.

The population of V beta 4+ T cells expands in the lungs of C57BL/6 mice infected with Histoplasma capsulatum, and the elimination of these cells impairs protective immunity. To determine the antigen or antigens that trigger their proliferation, V beta 4+ T cell hybridomas were generated from the lungs and spleens of infected mice. We mapped the antigenic determinants by T cell Western blot. Pulmonary and splenic T cells recognized 3 regions comprising <25, 55-70, and 125-140 kDa. The majority of hybridomas from lungs, but not from spleens, responded to the high molecular mass region. A protein from that area was identified, by amino acid sequencing, as a homologue of Sec31 from Saccharomyces cerevisiae. Vaccination with recombinant Sec31 reduced fungal burden and improved survival in mice, and its efficacy was critically dependent on the presence of V beta 4+ T cells. Thus, a homologue of Sec31 is a trigger of the expansion of the V beta 4+ T cell population and is important to the generation of protective immunity.

Protective efficacy of an oral vaccine to reduce carriage of Borrelia burgdorferi (strain N40) in mouse and tick reservoirs.

Lyme disease is caused by the spirochete Borrelia burgdorferi, which is transmitted through the bite of infected Ixodes ticks. Vaccination of mice with outer surface protein A (OspA) of B. burgdorferi has been shown to both protect mice against B. burgdorferi infection and reduce carriage of the organism in feeding ticks. Here we report the development of a murine-targeted OspA vaccine utilizing Vaccinia virus to interrupt transmission of disease in the reservoir hosts, thus reducing incidence of human disease. Oral vaccination of mice with a single dose of Vaccinia expressing OspA resulted in high antibody titers to OspA, 100% protection of vaccinated mice from infection with B. burgdorferi, and significant clearance of B. burgdorferi from infected ticks fed on vaccinated animals. The results indicate the vaccine is effective and may provide a manner to reduce incidence of Lyme disease.

A deficiency in gamma interferon or interleukin-10 modulates T-Cell-dependent responses to heat shock protein 60 from Histoplasma capsulatum.

Immunization of mice with heat shock protein 60 from Histoplasma capsulatum or a polypeptide from the protein designated F3 confers protection. Vbeta8.1/8.2+ T cells are critically important for the protective efficacy of this antigen. The production of interleukin-10 and gamma interferon following vaccination is essential for efficacy. In this study, we sought to determine whether the absence of either cytokine modified the repertoire of antigen-reactive T cells and whether it altered the functional properties of T cells. Mice lacking gamma interferon or interleukin-10 manifested a skewed repertoire compared to that of wild-type mice. The bias was most marked in gamma interferon-deficient mice and modestly altered in interleukin-10-deficient animals. The altered repertoire in gamma interferon-deficient mice could not be explained at the level of antigen presentation or by the absence of this population from mice. The proportion of T cells from interleukin-10-deficient mice manifesting a Th1 phenotype was greatly increased compared to that from wild-type animals. Transfer of splenocytes from gamma interferon- or interleukin-10-deficient mice immunized with heat shock protein 60 failed to confer protection in T-cell receptor alpha/beta-/- mice. The transfer of T-cell clones that did not produce both cytokines failed to prolong survival in T-cell receptor alpha/beta-/- mice, whereas the clones with the same features that were derived from wild-type mice did. These results indicate that the cytokine milieu influences the shape of the T-cell receptor repertoire and support the importance of gamma interferon and interleukin-10 in the efficacy of heat shock protein 60.

The protective immune response to heat shock protein 60 of Histoplasma capsulatum is mediated by a subset of V beta 8.1/8.2+ T cells.

Immunization with recombinant heat shock protein 60 (rHsp60) from Histoplasma capsulatum or a region of the protein designated fragment 3 (F3) confers protection from a subsequent challenge in mice. To determine the T cell repertoire involved in the response to Hsp60, T cell clones from C57BL/6 mice immunized with rHsp60 were generated and examined for Vbeta usage by flow cytometry and RT-PCR. Vbeta8.1/8.2(+) T cells were preferentially expanded; other clones bore Vbeta4, -6, or -11. When Vbeta8.1/8.2(+) cells were depleted in mice, Vbeta4(+) T cell clones were almost exclusively isolated. Measurement of cytokine production demonstrated that nine of 16 Vbeta8.1/8.2(+) clones were Th1, while only three of 13 non-Vbeta8.1/8.2(+) clones were Th1. In mice immunized with rHsp60, depletion of Vbeta8.1/8.2(+), but not Vbeta6(+) plus Vbeta7(+), T cells completely abolished the protective efficacy of Hsp60 to lethal and sublethal challenges. Examination of the TCR revealed that a subset of Vbeta8.1/2(+) clones that produced IFN-gamma and were reactive to F3 shared a common CDR3 sequence, DGGQG. Transfer of these T cell clones into TCR alpha/beta(-/-) or IFN-gamma(-/-) mice significantly improved survival, while transfer of other Vbeta8.1/8.2(+) clones that were F3 reactive but were Th2 or clones that were not reactive to F3 but were Th1 did not confer protection. These data indicate that a distinct subset of Vbeta8.1/8.2(+) T cells is crucial for the generation of a protective response to rHsp60.