Magnitude and diversity of immune response to vaccinia virus is dependent on route of administration

Pockenvirusinfektionen in der Dermatologie: Poxvirus infections in dermatology - the neglected, the notable, and the notorious

Die Familie Poxviridae umfasst derzeit 22 Gattungen, die Wirbeltiere infizieren können. Humanpathogene Pockenviren gehören den Gattungen Ortho‐, Para‐, Mollusci‐ und Yatapoxvirus an. Bis zur Eradikation der Variola vera im Jahr 1979 waren die Pocken, im Volksmund auch Blattern genannt, eine schwerwiegende Gesundheitsbedrohung für die Bevölkerung. Noch heute sind Dermatologen mit zahlreichen Pockenvirusinfektionen konfrontiert, wie den Bauernhofpocken, die als Zoonosen nach Tierkontakten in ländlichen Gebieten oder nach Massenversammlungen auftreten können. In den Tropen können Erkrankungen durch Tanapox‐ oder Vaccinia‐Viren zu den Differenzialdiagnosen gehören. Dellwarzen sind weltweit verbreitet und werden in bestimmten Fällen als sexuell übertragbare Pockenvirusinfektion angesehen. In jüngster Zeit hatten sich Mpox (Affenpocken) zu einer gesundheitlichen Notlage von internationaler Tragweite entwickelt, die eine rasche Identifizierung und angemessene Behandlung durch Dermatologen und Infektiologen erfordert. Fortschritte und neue Erkenntnisse über Epidemiologie, Diagnose, klinische Manifestationen und Komplikationen sowie Behandlung und Prävention von Pockenvirusinfektionen erfordern ein hohes Maß an Fachwissen und interdisziplinärer Zusammenarbeit in den Bereichen Virologie, Infektiologie und Dermatologie. Dieser CME‐Artikel bietet einen aktualisierten systematischen Überblick, um praktizierende Dermatologen bei der Identifizierung, Differenzialdiagnose und Behandlung klinisch relevanter Pockenvirusinfektionen zu unterstützen.

Poxvirus infections in dermatology - the neglected, the notable, and the notorious

The family Poxviridae currently comprises 22 genera that infect vertebrates. Of these, members of the Ortho-, Para-, Mollusci- and Yatapoxvirus genera have been associated with human diseases of high clinical relevance in dermatology. Historically, smallpox had been a notorious health threat until it was declared eradicated by the World Health Organization in 1979. Today, dermatologists are confronted with a variety of poxviral infections, such as farmyard pox, which occurs as a zoonotic infection after contact with animals. In the tropics, tanapox or vaccinia may be in the differential diagnosis as neglected tropical dermatoses. Molluscum contagiosum virus infection accounts for significant disease burden worldwide and is classified as a sexually transmitted infection in certain scenarios. Recently, mpox (monkeypox) has emerged as a public health emergency of international concern, requiring rapid recognition and appropriate management by dermatologists and infectious disease specialists. Advances and new insights into the epidemiology, diagnosis, clinical manifestations and complications, treatment, and prevention of poxviral infections require a high level of expertise and interdisciplinary skills from healthcare professionals linking virology, infectious diseases, and dermatology. This CME article provides a systematic overview and update to assist the practicing dermatologist in the identification, differential diagnosis, and management of poxviral infections.

Smallpox vaccination in a mouse model

The monkeypox epidemic, which became unusually widespread among humans in 2022, has brought awareness about the necessity of smallpox vaccination of patients in the risk groups. The modern smallpox vaccine variants are introduced either intramuscularly or by skin scarification. Intramuscular vaccination cannot elicit an active immune response, since tissues at the vaccination site are immunologically poor. Skin has evolved into an immunologically important organ in mammals; therefore, intradermal delivery of a vaccine can ensure reliable protective immunity. Historically, vaccine inoculation into scarified skin (the s.s. route) was the first immunization method. However, it does not allow accurate vaccine dosing, and high-dose vaccines need to be used to successfully complete this procedure. Intradermal (i.d.) vaccine injection, especially low-dose one, can be an alternative to the s.s. route. This study aimed to compare the s.s. and i.d. smallpox immunization routes in a mouse model when using prototypic second- and fourth-generation low-dose vaccines (104 pfu). Experiments were conducted using BALB/c mice; the LIVP or LIVP-GFP strains of the vaccinia virus (VACV) were administered into the tail skin via the s.s. or i.d. routes. After vaccination (7, 14, 21, 28, 42, and 56 days post inoculation (dpi)), blood samples were collected from the retro-orbital venous sinus; titers of VACV-specific IgM and IgG in the resulting sera were determined by ELISA. Both VACV strains caused more profound antibody production when injected via the i.d. route compared to s.s. inoculation. In order to assess the level of the elicited protective immunity, mice were intranasally infected with a highly lethal dose of the cowpox virus on 62 dpi. The results demonstrated that i.d. injection ensures a stronger protective immunity in mice compared to s.s. inoculation for both VACV variants.

Effect of the ati Gene Deletion on the Pathogenicity and Immunogenicity of the Vaccinia Virus

Among the nonvirion proteins of the vaccinia virus (VACV), a 94-kDa long protein is most abundantly present; the protein is a truncated form of the 150-kDa A-type inclusion (ATI) protein of the cowpox virus encoded by the ati gene. This VACV protein does not form intracellular ATIs, being as it is a major immunogen upon infection/immunization of humans or animals with the VACV. Antibodies specific to this protein are not virus-neutralizing. The present study focused on the effect of the production of this nonstructural major immunogenic VACV protein on the manifestation of pathogenicity and immunogenicity of the virus in the BALB/c mouse model of infection. In order to introduce a targeted deletion into the VACV LIVP genome, the recombinant integration/deletion plasmid pΔati was constructed and further used to generate the recombinant virus LIVPΔati. The pathogenicity of the VACV LIVP and LIVPΔati strains was studied in 3-week-old mice. The mice were intranasally infected with the viruses at a dose of 107 pfu; 50% of the animals infected with the parent LIVP strain died, while infection with the LIVPΔati strain led to the death of only 20% of the mice. Intradermal vaccination of mice aged 6- weeks with the LIVPΔati virus statistically significantly increased the production of VACV-specific IgG, compared to that after intradermal vaccination with VACV LIVP. Meanwhile, no differences were noted in the cell-mediated immune response to the vaccination of mice with VACV LIVP or LIVPΔati, which was assessed by ELISpot according to the number of splenocytes producing IFN-γ in response to stimulation with virus-specific peptides. Intranasal infection of mice with lethal doses of the cowpox virus or the ectromelia virus on day 60 post-immunization with the studied VACV variants demonstrated that the mutant LIVPΔati elicits a stronger protective response compared to the parent LIVP.

Comparison of the Effectiveness of Transepidemal and Intradermal Immunization of Mice with the Vacinia Virus

The spread of the monkeypox virus infection among humans in many countries outside of Africa, which started in 2022, is now drawing the attention of the medical and scientific communities to the fact that immunization against this infection is sorely needed. According to current guidelines, immunization of people with the first-generation smallpox vaccine based on the vaccinia virus (VACV) LIVP strain, which is licensed in Russia, should be performed via transepidermal inoculation (skin scarification, s.s.). However, the long past experience of using this vaccination technique suggests that it does not ensure virus inoculation into patients' skin with enough reliability. The procedure of intradermal (i.d.) injection of a vaccine can be an alternative to s.s. inoculation. The effectiveness of i.d. vaccination can depend on the virus injection site on the body. Therefore, the aim of this study was to compare the development of the humoral and cellular immune responses in BALB/c mice immunized with the LIVP VACV strain, which was administered either by s.s. inoculation or i.d. injection into the same tail region of the animal. A virus dose of 105 pfu was used in both cases. ELISA of serum samples revealed no significant difference in the dynamics and level of production of VACV-specific IgM and IgG after i.d. or s.s. vaccination. A ELISpot analysis of splenocytes from the vaccinated mice showed that i.d. administration of VACV LIVP to mice induces a significantly greater T-cell immune response compared to s.s. inoculation. In order to assess the protective potency, on day 45 post immunization, mice were intranasally infected with lethal doses of either the cowpox virus (CPXV) or the ectromelia virus (ECTV), which is evolutionarily distant from the VACV and CPXV. Both vaccination techniques ensured complete protection of mice against infection with the CPXV. However, when mice were infected with a highly virulent strain of ECTV, 50% survived in the i.d. immunized group, whereas only 17% survived in the s.s. immunized group. It appears, therefore, that i.d. injection of the VACV can elicit a more potent protective immunity against orthopoxviruses compared to the conventional s.s. technique.

The Route of Infection Influences the Contribution of Key Immunity Genes to Antibacterial Defense in Anopheles gambiae

Insect systemic immune responses to bacterial infections have been mainly studied using microinjections, whereby the microbe is directly injected into the hemocoel. While this methodology has been instrumental in defining immune signaling pathways and enzymatic cascades in the hemolymph, it remains unclear whether and to what extent the contribution of systemic immune defenses to host microbial resistance varies if bacteria invade the hemolymph after crossing the midgut epithelium subsequent to an oral infection. Here, we address this question using the pathogenic Serratia marcescens (Sm) DB11 strain to establish systemic infections of the malaria vector Anopheles gambiae, either by septic Sm injections or by midgut crossing after feeding on Sm. Using functional genetic studies by RNAi, we report that the two humoral immune factors, thioester-containing protein 1 and C-type lectin 4, which play key roles in defense against Gram-negative bacterial infections, are essential for defense against systemic Sm infections established through injection, but they become dispensable when Sm infects the hemolymph following oral infection. Similar results were observed for the mosquito Rel2 pathway. Surprisingly, blocking phagocytosis by cytochalasin D treatment did not affect mosquito susceptibility to Sm infections established through either route. Transcriptomic analysis of mosquito midguts and abdomens by RNA-seq revealed that the transcriptional response in these tissues is more pronounced in response to feeding on Sm. Functional classification of differentially expressed transcripts identified metabolic genes as the most represented class in response to both routes of infection, while immune genes were poorly regulated in both routes. We also report that Sm oral infections are associated with significant downregulation of several immune genes belonging to different families, specifically the clip-domain serine protease family. In sum, our findings reveal that the route of infection not only alters the contribution of key immunity genes to host antimicrobial defense but is also associated with different transcriptional responses in midguts and abdomens, possibly reflecting different adaptive strategies of the host.

Infection-Immunity Competition: A Simple Model for Illustrating the Background of Individual Response on Herd Immunity

For achieving herd immunity, the proportion of individuals who are immunized, and the proportion of susceptible individuals are normally regarded as the key factors. Here, it is discussed that the immunity is not a yes/no decision in all cases, but a limited (relative) immunity should be kept in mind. This effect would cause a dependence of infection from the level of immunity and the strength of single-infection impact events (virus load). As a result, a stepwise enhancement of low-level immunity could be achieved in case of infection contacts at low concentrations of infectious particles. This behavior is probably important for airborne infection paths. Therefore, it might play a role in the case of the recent SARS (new coronavirus) pandemic and could have a strong effect on herd immunity.