Validation of computer-assisted, pixel-based analysis of multiple-colour immunofluorescence histology

Laryngeal transplantation in minipigs: early immunological outcomes

Despite recent tissue-engineering advances, there is no effective way of replacing all the functions of the larynx in those requiring laryngectomy. A recent clinical transplant was a success. Using quantitative immunofluorescence targeted at immunologically relevant molecules, we have studied the early (48 h and 1 week) immunological responses within larynxes transplantated between seven pairs of National Institutes of Health (NIH) minipigs fully homozygous at the major histocompatibility complex (MHC) locus. There were only small changes in expression of some molecules (relative to interindividual variation) and these were clearest in samples from the subglottic region, where the areas of co-expression of CD25(+) CD45RC(-) CD8(-) and of CD163(+) CD172(+) MHC-II(-) increased at 1 week after transplant. In one case, infiltration by recipient T cells was analysed by T cell receptor (TCR) Vβ spectratype analysis; this suggested that changes in the T cell repertoire occur in the donor subglottis mucosal tissues from day 0 to day 7, but that the donor and recipient mucosal Vβ repertoires remain distinct. The observed lack of strong immunological responses to the trauma of surgery and ischaemia provides encouraging evidence to support clinical trials of laryngeal transplantation, and a basis on which to interpret future studies involving mismatches.

Neonatal colonisation expands a specific intestinal antigen-presenting cell subset prior to CD4 T-cell expansion, without altering T-cell repertoire

Interactions between the early-life colonising intestinal microbiota and the developing immune system are critical in determining the nature of immune responses in later life. Studies in neonatal animals in which this interaction can be examined are central to understanding the mechanisms by which the microbiota impacts on immune development and to developing therapies based on manipulation of the microbiome. The inbred piglet model represents a system that is comparable to human neonates and allows for control of the impact of maternal factors. Here we show that colonisation with a defined microbiota produces expansion of mucosal plasma cells and of T-lymphocytes without altering the repertoire of alpha beta T-cells in the intestine. Importantly, this is preceded by microbially-induced expansion of a signal regulatory protein α-positive (SIRPα⁺) antigen-presenting cell subset, whilst SIRPα⁻CD11R1⁺ antigen-presenting cells (APCs) are unaffected by colonisation. The central role of intestinal APCs in the induction and maintenance of mucosal immunity implicates SIRPα⁺ antigen-presenting cells as orchestrators of early-life mucosal immune development.

Follicular dendritic cell-specific prion protein (PrP) expression alone is sufficient to sustain prion infection in the spleen

Prion diseases are characterised by the accumulation of PrP^Sc, an abnormally folded isoform of the cellular prion protein (PrP^C), in affected tissues. Following peripheral exposure high levels of prion-specific PrP^Sc accumulate first upon follicular dendritic cells (FDC) in lymphoid tissues before spreading to the CNS. Expression of PrP^C is mandatory for cells to sustain prion infection and FDC appear to express high levels. However, whether FDC actively replicate prions or simply acquire them from other infected cells is uncertain. In the attempts to-date to establish the role of FDC in prion pathogenesis it was not possible to dissociate the Prnp expression of FDC from that of the nervous system and all other non-haematopoietic lineages. This is important as FDC may simply acquire prions after synthesis by other infected cells. To establish the role of FDC in prion pathogenesis transgenic mice were created in which PrP^C expression was specifically “switched on” or “off” only on FDC. We show that PrP^C-expression only on FDC is sufficient to sustain prion replication in the spleen. Furthermore, prion replication is blocked in the spleen when PrP^C-expression is specifically ablated only on FDC. These data definitively demonstrate that FDC are the essential sites of prion replication in lymphoid tissues. The demonstration that Prnp-ablation only on FDC blocked splenic prion accumulation without apparent consequences for FDC status represents a novel opportunity to prevent neuroinvasion by modulation of PrP^C expression on FDC.

Prion diseases are infectious neurological disorders and are considered to be caused by an abnormally folded infectious protein termed PrP^Sc. Soon after infection prions accumulate first upon follicular dendritic cells (FDC) in lymphoid tissues before spreading to the brain where they cause damage to nerve cells. Cells must express the normal cellular prion protein PrP^C to become infected with prions. However, whether FDC are infected with prions or simply acquire them from other infected cells is unknown. To establish the role of FDC in prion disease PrP^C expression was specifically “switched on” or “off” only on FDC. We show that PrP^C-expressing FDC alone are sufficient to sustain prion replication in the spleen. Furthermore, prion replication is blocked in the spleen when PrP^C-expression is switched off only on FDC. These data definitively demonstrate that FDC are the essential sites of prion replication in lymphoid tissues.

The effects of host age on the transport of complement-bound complexes to the spleen and the pathogenesis of intravenous scrapie infection

Infections with variant Creutzfeldt-Jakob disease (vCJD) have almost exclusively occurred in young patients, but the reasons for this age distribution are uncertain. Our data suggest that the pathogenesis of many peripherally acquired transmissible spongiform encephalopathy (TSE) agents is less efficient in aged individuals. Four vCJD cases linked to transfusion of vCJD-contaminated blood or blood products have been described. Three cases occurred in elderly patients, implying that intravenous exposure is more efficient in aged individuals than other peripheral routes. To test this hypothesis, young (6 to 8 weeks old) and aged (600 days old) mice were injected intravenously with a TSE agent. In aged and young mice, the intravenous route was more efficient than other peripheral routes of TSE agent exposure. However, in aged mice, disease pathogenesis was significantly reduced. Although most aged mice failed to develop clinical disease during their life spans, many showed histopathological signs of TSE disease in their brains. Thus, the effects of age on intravenous TSE pathogenesis may lead to significant levels of subclinical disease in the population. After peripheral exposure, many TSE agents accumulate upon follicular dendritic cells (FDCs) in lymphoid tissues before they infect the brain. In aged spleens, PrP(C) expression and TSE agent accumulation upon FDCs were reduced. Furthermore, the splenic marginal zone microarchitecture was substantially disturbed, adversely affecting the delivery of immune complexes to FDCs. This study is the first to suggest that the effects of aging on the microarchitecture and the function of the splenic marginal zone significantly influence the pathogenesis of an important pathogen.

Identification and characterisation of an iron-responsive candidate probiotic

Background

Iron is an essential cofactor in almost all biological systems. The lactic acid bacteria (LAB), frequently employed as probiotics, are unusual in having little or no requirement for iron. Iron in the human body is sequestered by transferrins and lactoferrin, limiting bacterial growth. An increase in the availability of iron in the intestine by bleeding, surgery, or under stress leads to an increase in the growth and virulence of many pathogens. Under these high iron conditions, LAB are rapidly out-competed; for the levels of probiotic bacteria to be maintained under high iron conditions they must be able to respond by increasing growth rate to compete with the normal flora. Despite this, iron-responsive genera are poorly characterised as probiotics.

Methodology/Principal Findings

Here, we show that a panel of probiotics are not able to respond to increased iron availability, and identify an isolate of Streptococcus thermophilus that can increase growth rate in response to increased iron availability. The isolate of S. thermophilus selected was able to reduce epithelial cell death as well as NF-κB signalling and IL-8 production triggered by pathogens. It was capable of crossing an epithelial cell barrier in conjunction with E. coli and downregulating Th1 and Th17 responses in primary human intestinal leukocytes.

Conclusions/Significance

We propose that an inability to compete with potential pathogens under conditions of high iron availability such as stress and trauma may contribute to the lack of efficacy of many LAB-based probiotics in treating disease. Therefore, we offer an alternative paradigm which considers that probiotics should be able to be competitive during periods of intestinal bleeding, trauma or stress.

Most B cells in non-lymphoid tissues are naïve

The current view of lymphocyte migration states that naïve lymphocytes re-circulate between the blood and the lymph via the lymph nodes, but are not able to access non-lymphoid tissues. We examined B lymphocytes in peripheral tissues and found that the majority were phenotypically similar to naïve B cells in lymphoid tissues and were located within the parenchyma, not associated with blood vessels. The mutation rate within the Vh region of these cells was substantially less than the rate attributed to somatic hypermutation and was identical to that observed in naïve B cells isolated from the lymph nodes, showing the presence of naïve B cells in the non-lymphoid organs. Further, using FTY720-treated mice, we showed that naïve B cells migrate through the peripheral tissues and, using pertussis toxin, that the entry of B cells was not controlled by chemokine-mediated signalling events. Overall, these results show that naïve B lymphocytes constitute the majority of the total B-cell population in non-lymphoid tissues and suggest that these cells may re-circulate through the periphery as part of their normal migration pathway. This has implications for the current view of the role of naïve B cells in priming and tolerance.

Direction of neutrophil movements by Campylobacter-infected intestinal epithelium

Campylobacter jejuni and Campylobacter coli together represent the leading bacterial cause of human enteritis. However, the pathogenesis of this disease is poorly understood. Infection results in the formation of crypt abscesses resulting from the migration of neutrophils across the intestinal epithelium and into the intestinal crypts. In this study, we model this process in vitro and show that Campylobacter infection of epithelium results in a quantifiable increase in the directed movement of neutrophils from the basolateral to apical surface of the epithelium. This process is dependent on both bacterially derived n-formyl peptides and on the host cell enzyme 12-lipoxygenase (12-LOX).

Image analysis to quantify histological and immunofluorescent staining of ex vivo skin and skin cell cultures

Image processing steps and analysis techniques were developed for the quantification of photomicrographs obtained from light and fluorescence microscopy. The substrates examined were either skin cell cultures, such as normal human keratinocytes (NHK) or fibroblasts, or ex vivo skin sections. Examples of the analyses are provided for the comparison of skincare active ingredient treated samples vs. placebo to demonstrate the utility of the methods to quantify and provide numerical data for a procedure that is typically qualitative in nature and based on observations by a histologist. Quantifiable experiments that are discussed include: Fontana Masson staining for melanin expression; Nile red staining to detect cellular lipid droplets; nuclei staining with diamidino-phenylindole (DAPI); and immunofluorescent staining of protein expression with a primary antibody directed against the protein (antigen) and a secondary antibody tagged with a fluorescent dye (Alexa Fluor 488) against the primary antibody.

Dendritic cells interact with CD4 T cells in intestinal mucosa

Absence of lymph nodes in nonmammalian species, expression of MHCII by APCs in the periphery, and the recent findings that T cells can change their polarization status after presentation in the lymph nodes imply a role for MHCII-mediated presentation outside the organized lymphoid tissue. This study shows that MHCII(+) ECs and DCs from the intestinal mucosa of the pig can present antigen to T cells in vitro. In vivo, APCs colocalize with T cells in pig and mouse intestinal mucosa. In the pig, endothelium is involved in these interactions in neonates but not in adults, indicating different roles for stromal and professional APCs in the neonate compared with the adult. The ratio of expression of DQ and DR MHCII locus products was lower on ECs than on other mucosal APCs, indicating that the two types of cells present different peptide sets. Adult nonendothelial APCs expressed a higher ratio of DQ/DR than in neonates. These results suggest that mucosal DCs can present antigen locally to primed T cells and that stromal APCs are recruited to these interactions in some cases. This raises the possibility that local presentation may influence T cell responses at the effector stage after initial presentation in the lymph node.

Rearing environment affects development of the immune system in neonates

Early-life exposure to appropriate microbial flora drives expansion and development of an efficient immune system. Aberrant development results in increased likelihood of allergic disease or increased susceptibility to infection. Thus, factors affecting microbial colonization may also affect the direction of immune responses in later life. There is a need for a manipulable animal model of environmental influences on the development of microbiota and the immune system during early life. We assessed the effects of rearing under low- (farm, sow) and high-hygiene (isolator, milk formula) conditions on intestinal microbiota and immune development in neonatal piglets, because they can be removed from the mother in the first 24 h for rearing under controlled conditions and, due to placental structure, neither antibody nor antigen is transferred in utero. Microbiota in both groups was similar between 2 and 5 days. However, by 12-28 days, piglets reared on the mother had more diverse flora than siblings reared in isolators. Dendritic cells accumulated in the intestinal mucosa in both groups, but more rapidly in isolator piglets. Importantly, the minority of 2-5-day-old farm piglets whose microbiota resembled that of an older (12-28-day-old) pig also accumulated dendritic cells earlier than the other farm-reared piglets. Consistent with dendritic cell control of T cell function, the effects on T cells occurred at later time-points, and mucosal T cells from high-hygiene, isolator pigs made less interleukin (IL)-4 while systemic T cells made more IL-2. Neonatal piglets may be a valuable model for studies of the effects of interaction between microbiota and immune development on allergy.

Primary porcine CD11R1+ antigen-presenting cells isolated from small intestinal mucosa mature but lose their T cell stimulatory function in response to cholera toxin treatment

Antigen-presenting cells (APCs) in the small intestinal mucosa perform dual functions of maintaining tissue homeostasis and of protecting against intestinal pathogens as key inducers of both innate and adaptive immune responses. Intestinal APCs are thus important regulators of intestinal immunity and also potential target cells for mucosal adjuvants such as cholera toxin (Ctx), which was used successfully in several oral vaccination studies in pigs. The aims of the present study were (1) to isolate porcine small intestinal APCs and evaluate the feasibility of using these cells for functional in vitro studies and (2) to determine the response of intestinal APCs to Ctx. Microscopic and flow cytometric analyses using antibodies to CD1, CD11R1, CD16, and SIRPalpha (SWC3) revealed the presence of multiple subsets of MHC-II(++) APCs in porcine small intestinal mucosa. The alpha-integrin subunit CD11R1 was most frequently expressed and therefore chosen as a selection marker. CD11R1(+) cells were enriched from total lamina propria cells to >90% purity by immunomagnetic separation. Within the CD11R1 cells, we identified two populations with distinct forward and side scatter characteristics: (1) APCs identified by their high expression of MHC-II and consisting of SIRPalpha(+) and SIRPalpha(-) subsets, and (2) contaminating eosinophils. In culture, intestinal APCs spontaneously matured, as shown by significant (>5-fold) increase in CD80/CD86 expression. The SIRPalpha(+) APCs quickly disappeared from the cultures, likely due to increased apoptotic cell death. However, the observed spontaneous changes in the isolated cell population did not mask the effects of stimulation with Ctx, which resulted in a 2.5-fold increase in the expression of maturation markers CD80/CD86, but significant loss of T cell stimulatory function, corroborating previous results obtained with MoDC.

At the crossroads: mucosal immunology of the larynx

The larynx sits at the crossroads between gastrointestinal and respiratory tracts. Besides its intrinsic importance in breathing, swallowing and voice production, the larynx is also exposed to unique immunological challenges. Given the propensity of chronic inflammatory conditions such as chronic laryngitis, which affects up to 20% of Western populations, it is surprising that our understanding of the immunology of this organ remains relatively limited. Recent work on the immunological architecture of the laryngeal mucosa, and its changes that result from external challenges and inflammatory conditions, provided valuable insight into the fascinating immunology of this organ. The lessons learnt from these investigations may go beyond devising improved therapy for chronic laryngeal inflammation. Establishing whether and how the laryngeal mucosa may be involved in the modulation of wider mucosal responses may provide novel routes to the treatment of inflammatory diseases of the respiratory and alimentary tracts such as asthma and inflammatory bowel disease.

Immunologic Response of the Laryngeal Mucosa to Extraesophageal Reflux

Objectives:

Extraesophageal reflux is common. The treatment costs are high, and there are associations with other diseases, including laryngeal cancer. Our studies of the mucosal immune response to this common inflammatory disease suggest an important role for the nonclassic antigen-presenting molecule CD1d in the response to inflammation. This study was performed to further explore the relationship between the CD1d–NKT cell–iGb3 axis and reflux.

Methods:

We carried out a prospective study of laryngeal biopsies from 12 patients with laryngopharyngeal reflux and 11 controls. Quantitative multiple-color immunofluorescence using antibodies for lymphocytes (CD3, CD161) and classic and nonclassic major histocompatibility complex (I, II, β2m, CD1d) was performed, and univariate and multivariate analysis and co-localization measurements were applied.

Results:

Epithelial major histocompatibility complex class I and II expression was unchanged by reflux, but expression of CD1d increased (p < 0.05; luminal layers) and confidence intervals diminished in the reflux group. Co-localization of NKT cells with CD1d increased in patients (p < 0.01); iGb3 exhibited strong expression throughout all layers of the laryngeal epithelium.

Conclusions:

These data indicate a role for the CD1d–NKT cell–iGb3 axis in response to extraesophageal reflux in humans. This represents a useful target for novel diagnostics and treatments for this common condition.

Phenotypical and morphological changes in the thymic microenvironment from ageing mice

The thymus is crucial for T-cell output and the age-associated involution of this organ, is thought to have a major impact in the decline in immunity that is seen in later life. The mechanism that underlines thymic involution is not known, however, we have evidence to suggest that this is may be due to changes in the thymic microenvironment. To further test this hypothesis, we quantified the in situ changes to markers that identify cortical and medullary thymic epithelial cells. This analysis revealed an age-dependent decline in cortical and medullary markers together with an increase in Notch and Delta expression, in older mice, as judged by immunohistochemistry. This was accompanied by alterations of the archetypal staining patterns and three dimensional analysis revealed changes in the morphology of the thymic microenvironment. These studies suggest that there are age-associated alterations in the thymic microenvironment, which may therefore play a role in thymic involution.

Aging and cancer-related loss of insulin-like growth factor 2 imprinting in the mouse and human prostate

Loss of imprinting (LOI) is an epigenetic alteration involving loss of parental origin-specific expression at normally imprinted genes. A LOI for Igf2, a paracrine growth factor, is important in cancer progression. Epigenetic modifications may be altered by environmental factors. However, is not known whether changes in imprinting occur with aging in prostate and other tissues susceptible to cancer development. We found a LOI for Igf2 occurs specifically in the mouse prostate associated with increased Igf2 expression during aging. In older animals, expression of the chromatin insulator protein CTCF and its binding to the Igf2-H19 imprint control region was reduced. Forced down-regulation of CTCF leads to Igf2 LOI. We further show that Igf2 LOI occurs with aging in histologically normal human prostate tissues and that this epigenetic alteration was more extensive in men with associated cancer. This finding may contribute to a postulated field of cancer susceptibility that occurs with aging. Moreover, Igf2 LOI may serve as a marker for the presence of prostate cancer.

The mucosal immune response to laryngopharyngeal reflux

RATIONALE

Laryngopharyngeal reflux (LPR) affects up to 20% of Western populations. Although individual morbidity is usually moderate, treatment costs are high and there are associations with other diseases, including laryngeal cancer. To date, there have been no studies of the mucosal immune response to this common inflammatory disease.

OBJECTIVES

To determine the mucosal immune response to LPR.

METHODS

We performed a prospective immunologic study of laryngeal biopsies from patients with LPR and control subjects (n = 12 and 11, respectively), and of primary laryngeal epithelial cells in vitro.

MEASUREMENTS AND MAIN RESULTS

Quantitative multiple-color immunofluorescence, using antibodies for lymphocytes (CD4, CD8, CD3, CD79, CD161), granulocytes (CD68, EMBP), monocytic cells (CD68, major histocompatibility complex [MHC] class II), and classical and nonclassical MHC (I, II, beta(2)-microglobulin, CD1d). Univariate and multivariate analysis and colocalization measurements were applied. There was an increase in percentage area of mucosal CD8(+) cells in the epithelium (P < 0.005), whereas other leukocyte and granulocyte antigens were unchanged. Although epithelial MHC class I and II expression was unchanged by reflux, expression of the nonclassical MHC molecule CD1d increased (P < 0.05, luminal layers). In vitro, laryngeal epithelial cells constitutively expressed CD1d. CD1d and MHC I expression were inversely related in all subjects, in a pattern which appears to be unique to the upper airway. Colocalization of natural killer T (NKT) cells with CD1d increased in patients (P < 0.01).

CONCLUSIONS

These data indicate a role for the CD1d-NKT cell axis in response to LPR in humans. This represents a useful target for novel diagnostics and treatments in this common condition.

Architectural changes in the thymus of aging mice

Age-associated thymic involution is one of the most dramatic and ubiquitous changes in the immune system, although the precise mechanisms involved still remain obscured. Several hypotheses have been proposed incorporating extrinsic and intrinsic factors, however, changes in the thymic microenvironment itself is one of the least investigated. We therefore decided to undertake a detailed histological examination of the aging thymus in order to elucidate possible mechanisms of thymic atrophy. This investigation provides insight into the changes within the murine thymus with age, demonstrating a new approach to quantify protein expressional differences while preserving the thymic architecture. There is a decline in expression of thymic epithelial cell-specific makers and an increase in fibroblast content in the aging mouse thymus. This is concurrent with a disorganization of the thymic compartments, a morphological transformation within the epithelial cells and alterations of their archetypal staining patterns. Furthermore, this is linked to a rise in apoptotic cells and the novel finding of increased senescence in the thymus of older mice that appears to be colocalized in the epithelial compartment. These changes within the thymic epithelial cells may be in part accountable for thymic atrophy and responsible for the decline in T-cell output.

Campylobacter and IFNgamma interact to cause a rapid loss of epithelial barrier integrity

BACKGROUND

The intestinal epithelium is a single layer of polarized cells and is the primary barrier separating foreign antigen and underlying lymphoid tissue. IFNgamma alters epithelial barrier function during inflammation by disrupting tight cell junctions and facilitating the paracellular transport of luminal antigens. The aim of this work was to determine whether Campylobacter infection of cells exposed to IFNgamma would lead to greater disruption of cell monolayers and hence increased bacterial translocation.

METHODS

Monolayers were polarized on Transwell polycarbonate membranes for 14 days and then cultured in the presence or absence of 100 U/mL IFNgamma. Campylobacter was added to the apical side of the monolayer at an MOI of 30. Transepithelial electrical resistance (TEER) was recorded and bacteria in the basal well counted every 2 hours. Cells were stained for occludin, actin, and nuclear DNA, and cell viability determined by measurement of apoptosis.

RESULTS

In the presence of IFNgamma, TEER dropped significantly after 18 hours, indicating a reduction in barrier function. A further significant decrease was seen in the presence of both IFNgamma and Campylobacter, indicating a synergistic effect, and cellular morphology and viability were affected. Bacterial translocation across the monolayer was also significantly greater in the presence of IFNgamma.

CONCLUSIONS

These combined effects indicate that Campylobacter infection concomitant with intestinal inflammation would result in a rapid and dramatic loss of epithelial barrier integrity, which may be a key event in the pathogenesis of Campylobacter-mediated colitis and the development of bloody diarrhea.

Interactions between immune cells and their microenvironment

In the past, studies of the immune system have identified molecules and cell types with immunological function and focussed on interactions between these components. However, it is increasingly apparent that the ability of immune cells to interact with elements from their microenvironment such as extracellular matrix components and stromal cells, that are often considered unlinked to the adaptive immune system, is central to the successful and correct functioning of the immune system. As a consequence, a number of sophisticated techniques have been used to analyse these interactions in vitro and in vivo. Here we describe the interactions involved in immune function and some of the methods used to examine them, focussing particularly on those that use imaging techniques.

Immune development in jejunal mucosa after colonization with selected commensal gut bacteria: a study in germ-free pigs

The immunological structure of the porcine jejunal lamina propria in germ-free piglets was compared with that of their counterparts associated with two strains of commensal Escherichia coli, A0 34/86 serotype O83:K24:H31 and the O86 E. coli strain, up to 20 days post-colonization. In the antigen-presenting compartment, both dendritic cells (DC) and cells expressing CD163, probably macrophages were investigated. In addition we also assessed the number of CD2+/CD3+ (T) cells. In contrast to some previous reports, we show a total lack of both DC and T cells for germ-free animals in the diffuse lymphoid tissue of villi and crypts of the jejunum. Association with either strain of commensal E. coli had a profound effect on the immune structure and resulted in extensive recruitment of DC to the lamina propria and of T cells to epithelium and lamina propria. The data suggest that the earliest immigrant cells were monocytes, which soon acquired the phenotype of mucosal DC. T cells migrated in at a slightly slower rate. Nevertheless, the response could be extremely rapid: within 3 days of colonization with O83, the magnitude of this response was comparable to that observed 20 days post-colonization.

Dynamics of infection and competition between two strains of Trypanosoma brucei brucei in the tsetse fly observed using fluorescent markers

Background

Genetic exchange occurs between Trypanosoma brucei strains during the complex developmental cycle in the tsetse vector, probably within the salivary glands. Successful mating will depend on the dynamics of co-infection with multiple strains, particularly if intraspecific competition occurs. We have previously used T. brucei expressing green fluorescent protein to study parasite development in the vector, enabling even one trypanosome to be visualized. Here we have used two different trypanosome strains transfected with either green or red fluorescent proteins to study the dynamics of co-infection directly in the tsetse fly.

Results

The majority of infected flies had both trypanosome strains present in the midgut, but the relative proportion of red and green trypanosome strains varied considerably between flies and between different sections of the midgut in individual flies. Colonization of the paired salivary glands revealed greater variability than for midguts, as each gland could be infected with red and/or green trypanosome strains in variable proportions. Salivary glands with a mixed infection appeared to have a higher density of trypanosomes than glands containing a single strain. Comparison of the numbers of red and green trypanosomes in the proventriculus, salivary exudate and glands from individual flies showed no correlation between the composition of the trypanosome population of the proventriculus and foregut and that of the salivary glands. For each compartment examined (midgut, foregut, salivary glands), there was a significantly higher proportion of mixed infections than expected, assuming the null hypothesis that the development of each trypanosome strain is independent.

Conclusion

Both the trypanosome strains used were fully capable of infecting tsetse, but the probabilities of infection with each strain were not independent, there being a significantly higher proportion of mixed infections than expected in each of three compartments examined: midgut, proventriculus and salivary glands. Hence there was no evidence of competition between trypanosome strains, but instead co-infection was frequent. Infection rates in co-infected flies were no different to those found routinely in flies infected with a single strain, ruling out the possibility that one strain enhanced infection with the other. We infer that each fly is either permissive or non-permissive of trypanosome infection with at least 3 sequential checkpoints imposed by the midgut, proventriculus and salivary glands. Salivary glands containing both trypanosome strains appeared to contain more trypanosomes than singly-infected glands, suggesting that lack of competition enhances the likelihood of genetic exchange.

Early immunological changes associated with laryngeal transplantation in a major histocompatibility complex-matched pig model

Laryngeal transplantation is an increasingly viable proposition for patients with irreversible diseases of the larynx. One human transplant has been performed successfully, but many questions remain before routine transplantation can begin. In order to measure the immunological changes in mismatched transplants, it is first necessary to know the immediate combined effects of ischaemia-reperfusion injury (IRI) plus the added insult of major surgery in a fully matched setting. We measured the changes in immunologically active mucosal cells following 3 h of cold ischaemia and 8 h of in situ reperfusion in a major histocompatibility complex (MHC)-matched minipig model (n = 4). Biopsies were prepared for quantitative, multiple-colour immunofluorescence histology. The number of immunologically active cells was significantly altered above (supraglottis) and below (subglottis) the vocal cords following transplantation and reperfusion (P < 0.05, P < 0.001, respectively). However, the direction of the change differed between the two subsites: cell numbers decreased post-transplant in the supraglottis and increased in the subglottis. Despite the statistical evidence for IRI, these changes were less than the large normal inter- and intrapig variation in cell counts. Therefore, the significance of IRI in exacerbating loss of function or rejection of a laryngeal allograft is open to question. Longer-term studies are required.

Major histocompatibility complex class I expression in human tonsillar and laryngeal epithelium

Understanding the immunological structure of the upper aerodigestive tract is important for analysing the interaction between incident challenges, such as human papillomavirus infection, and disease, particularly head and neck cancer. We have shown previously that tonsillar and laryngeal epithelium express major histocompatibility complex (MHC) class II locus products, but that expression of human leucocyte antigen (HLA)-DQ is reduced compared to HLA-DR. This may confer a decreased repertoire of presented T cell epitopes generated by the processing of exogenous peptides in upper airway mucosa. To determine whether the peptide repertoire presented by MHC class I loci varies in stratified squamous epithelium, laryngeal and tonsillar biopsies were taken from 19 otherwise healthy patients (M : F 6 : 13, 16-64 years). Quantitative immunofluorescence microscopy, using antibodies to MHC class I alpha-chain (pan-locus specific, HLA-A, HLA-B + C) and beta(2)-microglobulin, showed lower expression of the alpha-chain in laryngeal and tonsillar epithelium than in either lamina propria (tonsil 73% versus 89%, P < 0.0001; larynx 68% versus 85%, P < 0.005). Within the epithelium itself, the intensity of alpha-chain expression decreased from the basal to apical layers. In paired squamous epithelia from the two sites, alpha-chain expression was significantly higher in the tonsil compared to the larynx (79% versus 62%, P < 0.05). We suggest that these findings reflect functional stratification of these epithelia with the superficial layer, most exposed to incident challenges, less equipped to present antigens to conventional T cells. This may affect immunosurveillance directed at viral and tumour-related epitopes in the upper airway.

The postnatal development of the mucosal immune system and mucosal tolerance in domestic animals

The mucosal immune system is exposed to a range of antigens associated with pathogens, to which it must mount active immune responses. However, it is also exposed to a large number of harmless antigens associated with food and with commensal microbial flora, to which expression of active, inflammatory immune responses to these antigens is undesirable. The mucosal immune system must contain machinery capable of evaluating the antigens to which it is exposed and mounting appropriate effector or regulatory responses. Since the immune system is likely to have evolved initially in mucosal tissues, the requirement to prevent damaging allergic responses must be at least as old as the adaptive immune system, and studies of the mechanisms should include a range of non-mammalian species. Despite the importance for rational design of vaccines and for control of allergic reactions, the mechanisms involved are still largely unclear. It is not clear that the classical experimental protocol of "oral tolerance" is, in fact, measuring a biologically important phenomenon, nor is it clear whether tolerance is regulated in the evolutionarily recent organised lymphoid tissue (the lymph nodes) or the more ancient, diffuse architecture in the intestine. The capacity of the immune system to discriminate between "dangerous" and "harmless" antigens appears to develop with age and exposure to microbial flora. Thus, the ability of an individual or a group of animals to correctly regulate mucosal immune responses will depend on age, genetics and on their microbial environment and history. Attempts to manipulate the mucosal immune system towards active immune responses by oral vaccines, or towards oral tolerance, are likely to be confounded by environmentally-induced variability between individuals and between groups of animals.

Antigen presenting cells in mucosal sites of veterinary species

The ability of antigen presenting cells, in particular dendritic cells, to integrate a variety of environmental signals, together with their ability to respond appropriately by initiating either tolerance or defensive immune responses make them cells of particular relevance and importance in the mucosal environment. They have been demonstrated in a variety of mucosal tissues in veterinary species and have been characterized to varying degrees, showing that fundamental immunological principles apply throughout all species, but also highlighting some species differences. A major advantage of carrying out immunological research in veterinary species is their size: it is possible to cannulate lymphatic ducts and obtain information about cell migration between different tissues. It is also possible to obtain pure populations of relatively rare cell types such as the plasmacytoid dendritic cells or mucosal dendritic cells ex vivo for the study of immune responses to diseases in their natural host and for other thorough functional studies. Two major myeloid antigen presenting cell (APC) (dendritic cells, DC) cell populations have been described in gut draining lymph and other mucosal sites in ruminants and pigs, characterised by the presence or absence of surface molecules, their enzyme profiles, their ability to phagocytose and their different potential as APC. There is evidence that one of these subsets has migrated from the diffuse mucosal tissue, where it is found as a phagocytic as well as stimulatory APC population, which in turn may be derived from blood macrophages. In addition, the presence and role in viral infection of the IFN-alpha producing plasmacytoid DC in mucosal tissue is discussed, based on studies in pigs.