Regulatory T cells (Tregs) are a subset of T cells that are responsible for maintaining peripheral immune tolerance and homeostasis. The hallmark of Tregs is the expression of the forkhead box P3 (FoxP3) transcription factor. Natural regulatory T cells (nTregs) are a distinct population of T cells that express CD4 and FoxP3. nTregs develop in the thymus and function in maintaining peripheral immune tolerance. Other CD4+, CD4-CD8-, and CD8+CD28- T cells can be induced to acquire regulatory function by antigenic stimulation, depending on the cytokine milieu. Inducible (or adaptive) Tregs frequently express high levels of the interleukin 2 receptor (CD25). Atypical Tregs express FoxP3 and CD4 but have no surface expression of CD25. Type 1 regulatory T cells (Tr1 cells) produce IL-10, while T helper 3 cells (Th3) produce TGF-β. The function of inducible Tregs is presumably to maintain immune homeostasis, especially in the context of chronic inflammation or infection. Induction of Tregs in coronaviral infections protects against the more severe forms of the disease attributable to the host response. However, arteriviruses have exploited these T cell subsets as a means to dampen the immune response allowing for viral persistence. Treg induction or activation in the pathogenesis of disease has been described in both porcine reproductive and respiratory syndrome virus, lactate dehydrogenase elevating virus, and mouse hepatitis virus. This review discusses the development and biology of regulatory T cells in the context of arteriviral and coronaviral infection.

Theileria orientalis Ikeda genotype is a parasite that causes a disease in cattle that results in major economic issues in Asia, New Zealand, and Australia. The parasite is transmitted by Haemaphysalis longicornis ticks, which have recently been reported in numerous states throughout the eastern United States. Concurrently, cattle in Virginia showed clinical signs consistent with a hemoprotozoan infection. We used amplicons specific for the major piroplasm surface protein and small subunit rDNA of piroplasms to test blood samples from the cattle by PCR. Bidirectional Sanger sequencing showed sequences with 100% identity with T. orientalis Ikeda genotype 2 sequences. We detected the parasite in 3 unrelated herds and from various animals sampled at 2 time points. Although other benign T. orientalis genotypes are endemic to the United States, detection of T. orientalis Ikeda genotype might represent a risk for the cattle industry in Virginia.

The black-legged tick Ixodes scapularis Linnaeus (Acari: Ixodidae) is an important vector of microbial pathogens. Knowledge of the tick's innate immune response, particularly defensin and other antimicrobial peptides, is important for understanding how microbes survive in this tick. A defensin gene (slnA) from I. scapularis was obtained by reverse transcription-polymerase chain reaction (RT-PCR) using mRNA extracted from tissues of female ticks. RT-PCR indicated the gene was expressed in the midgut, haemocytes, and fat-body, although no evidence of a peptide was found. Sequencing a cloned cDNA fragment revealed a 225 bp open reading frame encoding a 74 amino acid pre-prodefensin, including the putative 38 amino acid mature peptide. Similarity between the defensin amino acid sequences of I. scapularis and Dermacentor variabilis (Say) (Acari: Ixodidae) was 62.2% for the pre-prodefensin region; for the mature defensins from these two species the similarity was 78.9%, with the six cysteine residues being located in the same relative position. PCR amplification and sequencing of chromosomal DNA suggests that slnA, along with vsnA, the defensin gene from D. variabilis, does not contain any introns. This is in contrast to the defensins described for the soft tick, Ornithodoros moubata (sensu Walton) (Acari: Argasidae). The role of defensin in the innate immune response of I. scapularis following microbial invasions is discussed.

Background Theileria orientalis is a tick-borne hemoparasite that causes anemia, ill thrift, and death in cattle globally. The Ikeda strain of T.orientalis is more virulent than other strains, leading to severe clinical signs and death of up to 5% of affected animals. Within the Asia–Pacific region, where it affects 25% of Australian cattle, T.orientalis Ikeda has a significant economic impact on the cattle industry. In 2017, T.orientalis Ikeda was detected in a cattle herd in Albermarle County, Virginia, United States. Months earlier, the U.S. was alerted to the invasion of the Asian longhorned tick, Haemaphysalis longicornis, throughout the eastern U.S. Abundant H.longicornis ticks were identified on cattle in the T.orientalis-affected herd in VA, and a subset of ticks from the environment were PCR-positive for T.orientalis Ikeda. A strain of T.orientalis from a previous U.S. outbreak was not transmissible by H.longicornis; however, H.longicornis is the primary tick vector of T.orientalis Ikeda in other regions of the world. Thus, the objective of this study was to determine whether invasive H.longicornis ticks in the U.S. are competent vectors of T.orientalis Ikeda. Methods Nymphal H.longicornis ticks were fed on a splenectomized calf infected with the VA-U.S.-T.orientalis Ikeda strain. After molting, a subset of adult ticks from this cohort were dissected, and salivary glands assayed for T.orientalis Ikeda via qPCR. The remaining adult ticks from the group were allowed to feed on three calves. Calves were subsequently monitored for T.orientalis Ikeda infection via blood smear cytology and PCR. Results After acquisition feeding on a VA-U.S.-T.orientalis Ikeda-infected calf as nymphs, a subset of molted adult tick salivary glands tested positive by qPCR for T.orientalis Ikeda. Adult ticks from the same cohort successfully transmitted T.orientalis Ikeda to 3/3 naïve calves, each of which developed parasitemia reaching 0.4–0.9%. Conclusions Our findings demonstrate that U.S. H.longicornis ticks are competent vectors of the VA-U.S.-T.orientalis Ikeda strain. This data provides important information for the U.S. cattle industry regarding the potential spread of this parasite and the necessity of enhanced surveillance and control measures.

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Melanoma in humans and dogs is considered highly immunogenic; however, the function of tumor-infiltrating lymphocytes (TILs) is often suppressed in the tumor microenvironment. In humans, current immunotherapies target checkpoint molecules (such as PD-L1, expressed by tumor cells), inhibiting their suppressive effect over TILs. The role of PD-L2, an alternative PD-1 ligand also overexpressed in malignant tumors and in patients with anti-PD-L1 resistance, remains poorly understood. In the current study, we evaluated the expression of checkpoint molecule mRNAs in canine melanoma and TILs. Analysis of checkpoint molecule gene expression was performed by RT-qPCR (real-time quantitative polymerase chain reaction) using total RNA isolated from formalin-fixed and paraffin-embedded melanomas ( n = 22) and melanocytomas ( n = 9) from the Virginia Tech Animal Laboratory Services archives. Analysis of checkpoint molecule expression revealed significantly higher levels of PDCD1 ( PD-1) and CD274 ( PD-L1) mRNAs and an upward trend in PDCD1LG2 ( PD-L2) mRNA in melanomas relative to melanocytomas. Immunohistochemistry revealed markedly increased numbers of CD3+ T cells in the highest PD-1-expressing subgroup of melanomas compared to the lowest PD-1 expressors, whereas densities of IBA1+ cells (macrophages) were similar in both groups. CD79a+ cell numbers were low for both groups. As in human melanoma, overexpression of the PD-1/PD-L1/PD-L2 axis is a common feature of canine melanoma. High expression of PD-1 and PD-L1 correlates with increased numbers of CD3+ cells. Additionally, the high level of IBA1+ cells in melanomas with low PD-1 expression and low CD3+ cells levels suggest that the expression of checkpoint molecules is modulated by interactions between T cells and cancer cells rather than histiocytes.

. The transcript sequence of the Amblyomma americanum Linnaeus (Acari: Ixodidae) defensin, termed amercin ( amn ), was ascertained and a 219-bp amn coding region identified. The gene encodes a 72-amino acid prepropeptide with a putative 37-amino acid mature peptide. This gene shows little similarity to either of the defensins from Amblyomma hebraeum Koch, the only other Amblyomma species for which a defensin has been described. Sequence comparisons with other tick defensins reveal amn to be shorter (6 bp or 2 amino acids) than the Ixodes scapularis Linnaeus (Acari: Ixodidae) and Dermacentor variabilis (Say) (Acari: Ixodidae) defensin sequences. The amercin prepropeptide has 60.8% and 59.5% similarity with the I. scapularis and D. variabilis prepropeptides, respectively, whereas the mature amercin peptide has 73.7% and 71.1% similarity with the mature peptides of these ticks. Similarity with other tick defensins ranges from 42% to 71%. In A. americanum , defensin transcript was found in the midgut, fat body and salivary gland tissues, as well as in the haemocytes. Defensin transcript was also present in early-stage eggs (less than 48 h old), late-stage eggs (approximately 2 weeks old), larvae and nymphs of A. americanum and I. scapularis , both of which are vector-competent for Borrelia spirochetes.