The detection of long-lasting memory foot-and-mouth disease (FMD) virus serotype O-specific CD4+ T cells from FMD-vaccinated cattle by bovine major histocompatibility complex class II tetramer

Are CD45RO+ and CD45RA- genuine markers for bovine memory T cells?

Effective vaccination induces memory T cells, which protect the host against pathogen re-infections. Therefore, detection of memory T cells is essential for evaluating vaccine efficacy, which was originally dependent on cytokine induction assays. Currently, two isoforms of CD45 tyrosine phosphatase, CD45RO expression and CD45RA exclusion (CD45RO+/ CD45RA-) are used extensively for detecting memory T cells in cattle. The CD45RO+/CD45RA- markers were first established in humans around three decades ago, and were adopted in cattle soon after. However, in the last two decades, some published data in humans have challenged the initial paradigm, and required multiple markers for identifying memory T cells. On the contrary, memory T cell detection in cattle still mostly relies on CD45RO+/CD45RA- despite some controversial evidence. In this review, we summarized the current literature to examine if CD45RO+/CD45RA- are valid markers for detecting memory T cells in cattle. It seems CD45RA and CD45RO (CD45RA/RO) as markers for identifying bovine memory T cells are questionable.

Assessment on Different Vaccine Formulation Parameters in the Protection against Heterologous Challenge with FMDV in Cattle

Foot-and-mouth disease (FMD) remains one of the major threats to animal health worldwide. Its causative agent, the FMD virus (FMDV), affects cloven-hoofed animals, including farm animals and wildlife species, inflicting severe damage to the international trade and livestock industry. FMDV antigenic variability remains one of the biggest challenges for vaccine-based control strategies. The current study analyzed the host’s adaptive immune responses in cattle immunized with different vaccine protocols and investigated its associations with the clinical outcome after infection with a heterologous strain of FMDV. The results showed that antigenic payload, multivalency, and revaccination may impact on the clinical outcome after heterologous challenge with FMDV. Protection from the experimental infection was related to qualitative traits of the elicited antibodies, such as avidity, IgG isotype composition, and specificity diversity, modulating and reflecting the vaccine-induced maturation of the humoral response. The correlation analyses of the serum avidity obtained per vaccinated individual might suggest that conventional vaccination can induce high-affinity immunoglobulins against conserved epitopes even within different FMDV serotypes. Cross-reaction among strains by these high-affinity antibodies may support further protection against a heterologous infection with FMDV.

Differential Expression of CD45RO and CD45RA in Bovine T Cells

Effective vaccination induces immune memory to protect animals upon pathogen re-encounter. Despite contradictory reports, bovine memory T cells are identified based on two isoforms of CD45, expression of CD45RO plus exclusion of CD45RA. In this report, we contrasted CD45RA/RO expression on circulatory T cells with IFNγ and IL4 expression induced by a conventional method. To our surprise, 20% of cattle from an enclosed herd did not express CD45RO on T cells without any significant difference on CD45RA expression and IFNγ or IL4 induction. In CD45RO expressing cattle, CD45RA and CD45RO expressions excluded each other, with dominant CD45RO (>90%) expression on gamma delta (γδ) followed by CD4+ (60%) but significantly higher CD45RA expression on CD8+ T cells (about 80%). Importantly, more than 80% of CD45RO expressing CD4+ and CD8+ T cells failed to produce IFNγ and IL-4; however, within the cytokine inducing cells, CD4+ T cells highly expressed CD45RO but those within CD8+ T cells mostly expressed CD45RA. Hence, CD45RO is not ubiquitously expressed in cattle, and rather than with memory phenotype, CD45RA/RO expression are more associated with distinct T cell subtypes.

Susceptibility to foot and mouth disease virus infection in vaccinated cattle, and host BoLA A and BoLA DRB3 genes polymorphism

The vaccination of the susceptible animal population against FMDV remains the most important measure to control the virus and prevent economic loss. Occurrence of infection in vaccinated animals is well-known in some diseases and is termed as breakthrough infection. The reasons include host genetic factors which can play an important role resulting in differences in susceptibility of animals to virus infection even with vaccine induced protective immune response. The Major Histocompatibility Complex (MHC) of bovines i.e. Bovine Leukocyte Antigen (BoLA) is important for antigen presentation. The BoLA DRB3 allele, which codes for the beta chain in Class II antigen, has been extensively studied and numerous reports have previously shown association of polymorphism in the gene with resistance/ susceptibility to several bacterial and viral diseases. In addition, previous studies have shown relationship between BoLA Class I and resistance or susceptibility to different diseases in cattle. The present study investigated the polymorphism in BoLA DRB3 and BoLA gene sequences of host and their relation with breakthrough FMDV infection in vaccinated animals. The study has identified three polymorphic sites each in both the genes which correlate with evidence of recent infection indicating their role in determining susceptibility of vaccinated animals to FMDV infection. Our limited study was performed on a relatively small samples size collected from one region of country. Further validation would require more detailed investigations on larger sample size.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13337-021-00754-8.