Infiltrating gamma delta T-cells and selectin endothelial ligands in the cutaneous phytohaemagglutinin-induced inflammatory reaction

γδ T cells in artiodactyls: Focus on swine

Vaccination is the most effective medical strategy for disease prevention but there is a need to improve livestock vaccine efficacy. Understanding the structure of the immune system of swine, which are considered a γδ T cell "high" species, and thus, particularly how to engage their γδ T cells for immune responses, may allow for development of vaccine optimization strategies. The propensity of γδ T cells to home to specific tissues, secrete pro-inflammatory and regulatory cytokines, exhibit memory or recall responses and even function as antigen-presenting cells for αβ T cells supports the concept that they have enormous potential for priming by next generation vaccine constructs to contribute to protective immunity. γδ T cells exhibit several innate-like antigen recognition properties including the ability to recognize antigen in the absence of presentation via major histocompatibility complex (MHC) molecules enabling γδ T cells to recognize an array of peptides but also non-peptide antigens in a T cell receptor-dependent manner. γδ T cell subpopulations in ruminants and swine can be distinguished based on differential expression of the hybrid co-receptor and pattern recognition receptors (PRR) known as workshop cluster 1 (WC1). Expression of various PRR and other innate-like immune receptors diversifies the antigen recognition potential of γδ T cells. Finally, γδ T cells in livestock are potent producers of critical master regulator cytokines such as interferon (IFN)-γ and interleukin (IL)-17, whose production orchestrates downstream cytokine and chemokine production by other cells, thereby shaping the immune response as a whole. Our knowledge of the biology, receptor expression and response to infectious diseases by swine γδ T cells is reviewed here.

Subpopulations of swine γδ T cells defined by TCRγ and WC1 gene expression

γδ T cells constitute a major portion of lymphocytes in the blood of both ruminants and swine. Subpopulations of swine γδ T cells have been distinguished by CD2 and CD8α expression. However, it was not clear if they have distinct expression profiles of their T-cell receptor (TCR) or WC1 genes. Identifying receptor expression will contribute to understanding the functional differences between these subpopulations and their contributions to immune protection. Here, we annotated three genomic assemblies of the swine TCRγ gene locus finding four gene cassettes containing C, J and V genes, although some haplotypes carried a null TRGC gene (TRGC4). Genes in the TRGC1 cassette were homologs of bovine TRGC5 cassette while the others were not homologous to bovine genes. Here we evaluated three principal populations of γδ T cells (CD2⁺/SWC5^-, CD2^-/SWC5⁺, and CD2^-/SWC5^-). Both CD2^- subpopulations transcribed WC1 co-receptor genes, albeit with different patterns of gene expression but CD2⁺ cells did not. All subpopulations transcribed TCR genes from all four cassettes, although there were differences in expression levels. Finally, the CD2⁺ and CD2^- γδ T-cell populations differed in their representation in various organs and tissues, presumably at least partially reflective of different ligand specificities for their receptors.

Maternal and dietary carotenoids interactively affect cutaneous basophil responses in growing chickens (Gallus gallus domesticus)

This trial examined effects of lutein supplied from maternal (i.e., in ovo) and dietary routes on cutaneous basophil hypersensitivity responses in chickens. Chicks hatched from one of two in ovo carotenoid levels (n=100/level; carotenoid-replete or carotenoid-deplete eggs) were fed one of two diet lutein levels (0 or 40 mg diet lutein/kg diet). At 14 d post-hatch, phytohemagglutinin (PHA) was injected into the wing web, and thickness and leukocyte populations were measured at 0 to 48 h. PHA increased wing web thickness at 4 to 48 h post-PHA (p<0.05), and the swelling response was most related to macrophage numbers in the wing web. Swelling occurred more rapidly in chicks from carotenoid-deplete eggs (p<0.05), but eventually reached a greater thickness in chicks from carotenoid-replete eggs (p<0.05). Differences in leukocyte infiltration occurred due to diet and in ovo carotenoid exposure, and indicate that pre- and post-hatch carotenoid exposure had additive or synergistic effects on the PHA-induced wing web response. Evaluation of the cellular contents of the injection site is a much better indicator of the immunomodulatory effects of lutein than measurements of the amount of swelling.

Porcine γδ T cells: Possible roles on the innate and adaptive immune responses following virus infection

gammadelta T cells recognise different types of antigen in alternative ways to alphabeta T cells, and thus appear to play a complementary role in the immune response. However, unlike alphabeta T cells, the role or function of gammadelta T cells is still unclear. As pigs possess a high proportion of circulating gammadelta T cells, they are suitable large animal model to study gammadelta T cell functions. This as yet has not been fully exploited, leaving porcine gammadelta T cell biology and its role in immunity in its infancy. Foot-and-mouth disease (FMD) high potency "emergency" vaccines are able to induce early protection from challenge and it has been suggested that, in part, there is some involvement of innate immune responses. The antigen component of the vaccine is able to stimulate purified naive pig gammadelta T cells and induce the mRNA of various cytokines and chemokines. This observation suggests that gammadelta T cells probably contribute to the early phase of the immune responses to FMD vaccination, and perhaps infection. A subset of these circulating gammadelta T cells display a phenotype similar to professional antigen presenting cells and are able to take up and present soluble antigen to CD4(+) T cells in a direct cell-cell interaction via MHC class II. This direct interaction between gammadelta T cells and CD4(+) T cells is likely to have a significant influence on the out come of the adaptive immune response.

L-Selectin ligands in lymphoid tissues and models of inflammation

Both lymphocyte recirculation through the lymphoid tissues and leukocyte recruitment to sites of inflammation are essential components of immune surveillance, and are necessary for sustained protection against pathogens. This process is mediated by the leukocyte-endothelial adhesion cascade of which the interaction of leukocyte L-Selectin with its endothelial ligand initiates the first critical tethering and rolling step. As well as discussing the constitutive L-Selectin ligands in lymphoid tissues, this review examines the literature regarding their induction in inflammation, and draws attention to recent findings regarding soluble L-Selectin ligands that suggest an emerging multifunctional role in leukocyte recirculation and inflammation.

Leucocyte entry and endothelial E-selectin expression following intradermal Propionibacterium acnes administration

Immune responses in porcine skin to intradermal inoculation of heat-killed Propionibacterium acnes (HKPA), the major bacterial agent associated with human inflammatory acne, were studied. Pigs were chosen as experimental animals because their skin is similar in structure and composition to that of man and because the use of genetically inbred pigs enables leucocytes to be transferred between animals without eliciting rejection responses. Two pigs were sensitized intradermally with 10 mg of HKPA and were challenged 2 weeks later with doses ranging from 1-100 microg of HKPA in various intradermal sites on the ventral aspect of the abdomen. Four further pigs, previously sensitized with Bacillus Calmette-Guérin (BCG) but not HKPA, were challenged with purified protein derivative (PPD) of bovine tuberculin and HKPA. Entry of(51)Cr-labelled peripheral blood lymphocytes (PBLs) over 48 h was studied in all the challenge sites. Peak PBL entry occurred at 4 h, remaining sustained up to 24 h. There was a dose-dependent effect of HKPA on the level of PBL entry, which was antigen-specific, as few leucocytes were seen in PPD-challenge sites in HKPA-sensitized pigs or in HKPA-challenged sites in BCG-sensitized pigs. There was also a substantial influx of(111)Indium-labelled neutrophils into the lesions. Lymphocytes present were predominantly of the CD3(+)CD2(+)T-cell subset, although gammadelta TCR(+)cells were present also, particularly after 24 h. E-selectin was markedly upregulated on dermal endothelium in the P. acnes sites. The histological infiltration and kinetics were similar to those reported in human inflammatory acne.

Effect of peroral anti-bacterial antiserum treatment on intestinal immune parameters of germ-free piglets intragastrically infected with virulent Salmonella typhimurium or enteropathogenic E. coli

Germ-free piglets were orally infected with either enteropathogenic E. coli 055 or a virulent strain of Salmonella typhimurium. Orally applied antiserum against E. coli protected infected animals in spite of the fact that the bacteria were consistently found in mesenteric lymph nodes and other organs. By contrast, the application of an antiserum against S. typhimurium was without any effect on the outcome of infection. The treatment with anti-bacterial antiserum prevented inflammation of ileal mucosa (TNF-alpha and heat shock protein 65 expression) only in piglets infected with E. coli. A decrease in the frequency of ileal MAC320+ cells was observed in all infected piglets treated with antiserum.

Cellular changes and cytokine expression in the ilea of gnotobiotic piglets resulting from peroral Salmonella typhimurium challenge

Two stable rough mutants of Salmonella spp. were studied as live peroral vaccines. The SF1591 mutant of S. typhimurium (Ra chemotype) protected germ-free piglets against subsequent infection with virulent smooth S. typhimurium LT2, whereas a deep-rough mutant of S. minnesota mR595 (Re chemotype) did not. We investigated cytokine and leukocyte profiles in the ilea of gnotobiotic piglets colonized for 1 week either with rough mutants alone or with rough mutants followed by S. typhimurium LT2. The ileal mucosae of piglets associated with strain SF1591 alone were not inflamed. Villi contained activated macrophages, and enterocytes expressed transforming growth factor beta (TGF-beta). Subsequent infection of piglets with S. typhimurium LT2 resulted in immigration of alphabeta T cells and immunoglobulin A (IgA) response. In contrast, the ileal mucosae of piglets associated with strain mR595 alone expressed heat shock proteins and inflammatory cytokines but not TGF-beta. Acellular villi contained numerous gammadelta T cells but no alphabeta T cells. After subsequent challenge with the LT2 strain, most piglets died of sepsis. Intestinal mucosae contained IgG but no IgA. These findings suggest the importance of cytokine signals in the regulation of intestinal responses against Salmonella infection.

Leucocyte and endothelial cell adhesion molecule expression in porcine histiocytic leiomyofibrosarcoma

A histiocytic sarcoma was present at birth in a pig. On the basis of ultra-structure and structural-protein composition (presence of alpha-smooth-muscle actin but not keratin), the sarcoma component was identified as a leiomyofibrosarcoma. Lipid-laden macrophages (histiocytes), which permeated the tumour in an apparently random fashion, were somewhat atypical in that they were negative for some macrophage markers; they gave a reaction, however, for CDw14. Despite its aggressive metastatic capacity, this tumour occurred almost exclusively in the subcutis, dermis and skeletal muscle. The tumour was extensively vascularized with many small capillaries which did not express E-selectin (CD69E), MHC class II or the L-selectin (CD69L) ligand, markers characteristic of inflamed (activated) endothelial cells in pig skin. Significant numbers of the histiocytes were positive for the integrins CD18 and VLA-4 (CD49d), indicating involvement of integrin pathways in the spread or growth, or both, of the leiomyofibrosarcoma. Most of the fibrous sarcoma cells also had extensive reactivity with an antibody to the standard variant form of CD44 (CD44s).

Constitutive and inflammatory lymphocyte trafficking

Here we provide a brief overview of lymphocyte trafficking with particular emphasis on the current state of knowledge in the pig. We discuss how the emphasis of research has changed since early studies in the 1960s and outline the current hypothesis of a multistep cascade for lymphocyte migration through specialized endothelia. During the last several years our research has focused mainly on lymphocyte migration in vivo. The inbred Babraham herd of MHC homozygous Large White pigs has allowed study of entry of either labelled (FITC or 51Cr) or unlabelled CD45 allotype-different donor lymphocytes and their subsets into various lymphoid, non-lymphoid and inflammatory tissues. The findings are considered under three different categories. Firstly, constitutive lymphocyte entry via 'high endothelial venules' (HEV-mediated), secondly, non-HEV-mediated lymphocyte homing and thirdly, lymphocyte entry into several models of inflammation with particular reference to the role of E-selectin. These findings demonstrate and underline the complexity and heterogeneity of lymphocyte homing, both at the whole population and subset level and yet, whilst a major step forward, the current hypotheses are perhaps too simple to explain much of this heterogeneity.

Transfer of T-cell-mediated, antigen-specific delayed type hypersensitivity reactions to naive recipient inbred pigs

Using inbred major histocompatibility complex-homozygous SLAb/b pigs, delayed-type hypersensitivity (DTH) reactions against either intradermal tuberculin (PPD) or topical 2,4-dinitro-1-fluorobenzene (DNFB) were transferred specifically by the intravenous injection of approximately 6 x 10(8) blood lymphocytes kg-1 bodyweight from donors sensitised, respectively, either with BCG or with DNFB into three-week-old piglets from an inbred litter. This antigen-specific, passively acquired sensitivity was revealed by three measures of DTH reactivity: first, macroscopic inflammation, which developed at the rate and intensity expected for actively acquired sensitivity to DNFB or PPD in older pigs; secondly, similarly enhanced local specific uptake of intravenously injected 51Cr-labelled normal lymphocytes (more than 35-fold for each); and, thirdly, histological evidence of markedly increased local infiltration of CD45+ lymphocytes and polymorphs, endothelial activation and the expression of adhesion molecules.

Noninvasive imaging of E-selectin expression by activated endothelium in urate crystal-induced arthritis

OBJECTIVE

To assess the expression of the cytokine-inducible endothelial leukocyte adhesion molecule E-selectin during the evolution of urate crystal-induced arthritis, using a recently described radiolabeled monoclonal antibody (MAb) imaging technique.

METHODS

Monosodium urate (MSU) crystals and saline alone were injected respectively into the right (inflamed) and left (control) knees of 3 young pigs. Four hours later, 111In-labeled 1.2B6 F(ab')2 (anti-E-selectin MAb) and 125I-labeled MOPC 21 F(ab')2 (control MAb) were injected intravenously. Uptake of 1.2B6 in inflamed and control joints was assessed by scintigraphy 7 and 24 hours after intraarticular injection of MSU crystals. Immunohistochemistry studies and radioactivity counting of tissues were performed postmortem to confirm the observations from scintigraphy.

RESULTS

MAb 1.2B6 F(ab')2 scintigraphic images of the knees revealed a significantly increased uptake in the right (inflamed) knee at 7 and 24 hours postinjection, particularly over the joint space. These in vivo images were consistent with E-selectin expression in the inflamed tissue detected by immunohistochemistry and with radioactivity counts postmortem. The synovial localization ratio (inflamed:control synovium counts) was 25.4 +/- 9.7 (mean +/- SD) for the anti-E-selectin MAb compared with 2.5 +/- 0.9 for the control MAb (P < 0.05, by paired Student's t-test).

CONCLUSION

E-selectin is expressed by synovial endothelium during the evolution of urate crystal-induced arthritis and can be detected noninvasively using a radiolabeled MAb. This E-selectin imaging technique has considerable potential for the noninvasive assessment of endothelial activation in arthritis and other inflammatory rheumatic diseases.

Lymphoid tissue structure and lymphocyte trafficking in the pig

The organised lymphoid tissues of the pig, though conventionally mammalian in most respects, show several distinctive properties in their structure and physiology. Specialised antigen-presenting lymphoid organs function at three compartmental levels: the body surfaces, their draining lymph nodes and the spleen in the bloodstream. Other organs act as lymphocytic depots and sites of phagocytosis of debris. Pig lymphocytes recirculate continuously through these organs and through different forms of inflammatory change, experimentally induced by mitogens and cytokines, using a spectrum of distinctively different physiological mechanisms. These tissues in the young pig differ both in the resting and activated cell subsets and the molecules involved, many of which remain to be completely defined. Intriguing insights are evident in the subtlety of regulation of the specificity, level and foetal ontogeny of trafficking mechanisms in these different tissues, though they are as yet poorly explained. This subtle molecular physiology is only now emerging because appropriate monoclonal antibody reagents are being developed and rigorous attention is being paid to the use of gentle physiological methods in experiments in vivo.

The Null/gamma delta TCR+ T cell family in the pig

The very large population of highly thymus-dependent, non-adherent 'Null' blood lymphocytes in young pigs, which lack most surface markers characteristic of classical T-cell subsets, have recently been shown to bear several novel population- and subset-specific antigens and gamma delta T-cell receptors. These T-lymphocytes differ radically from conventional CD2-positive T-cells in their origins, biological lifespan, tissue distribution, migration behaviour, cell surface phenotype, immunological responsiveness and mechanisms of trafficking through constitutive lymphoid tissues and inflammatory lesions. Elucidation of the roles of these enigmatic cells and their characteristic surface macromolecules in the initiation and regulation of immune functions promises to reveal much of fascination.