Heterogeneity and biased T cell receptor alpha/beta repertoire of mucosal CD8+ cells from murine large intestine: implications for functional state

Intraepithelial T Cells Diverge by Intestinal Location as Pigs Age

T cells resident within the intestinal epithelium play a central role in barrier integrity and provide a first line of immune defense. Intraepithelial T cells (IETs) are among the earliest immune cells to populate and protect intestinal tissues, thereby giving them an important role in shaping gut health early in life. In pigs, IETs are poorly defined, and their maturation in young pigs has not been well-studied. Given the importance of IETs in contributing to early life and long-term intestinal health through interactions with epithelial cells, the microbiota, and additional environmental factors, a deeper characterization of IETs in pigs is warranted. The objective of this study was to analyze age- and intestinal location-dependent changes in IETs across multiple sites of the small and large intestine in pigs between 4- and 8-weeks of age. IETs increased in abundance over time and belonged to both γδ and αβ T cell lineages. Similar compositions of IETs were identified across intestinal sites in 4-week-old pigs, but compositions diverged between intestinal sites as pigs aged. CD2⁺CD8α⁺ γδ T cells and CD4^-CD8α⁺ αβ T cells comprised >78% of total IETs at all intestinal locations and ages examined. Greater percentages of γδ IETs were present in large intestine compared to small intestine in older pigs. Small intestinal tissues had greater percentages of CD2⁺CD8α^- γδ IETs, while CD2⁺CD8α⁺ γδ IET percentages were greater in the large intestine. Percentages of CD4^-CD8α⁺ αβ IETs increased over time across all intestinal sites. Moreover, percentages of CD27⁺ cells decreased in ileum and large intestine over time, indicating increased IET activation as pigs aged. Percentages of CD27⁺ cells were also higher in small intestine compared to large intestine at later timepoints. Results herein emphasize 4- to 8-weeks of age as a critical window of IET maturation and suggest strong associations between intestinal location and age with IET heterogeneity in pigs.

Regionalized Development and Maintenance of the Intestinal Adaptive Immune Landscape

The intestinal immune system has the daunting task of protecting us from pathogenic insults while limiting inflammatory responses against the resident commensal microbiota and providing tolerance to food antigens. This role is particularly impressive when one considers the vast mucosal surface and changing landscape that the intestinal immune system must monitor. In this review, we highlight regional differences in the development and composition of the adaptive immune landscape of the intestine and the impact of local intrinsic and environmental factors that shape this process. To conclude, we review the evidence for a critical window of opportunity for early-life exposures that affect immune development and alter disease susceptibility later in life.

Regional specialization within the intestinal immune system

The intestine represents the largest compartment of the immune system. It is continually exposed to antigens and immunomodulatory agents from the diet and the commensal microbiota, and it is the port of entry for many clinically important pathogens. Intestinal immune processes are also increasingly implicated in controlling disease development elsewhere in the body. In this Review, we detail the anatomical and physiological distinctions that are observed in the small and large intestines, and we suggest how these may account for the diversity in the immune apparatus that is seen throughout the intestine. We describe how the distribution of innate, adaptive and innate-like immune cells varies in different segments of the intestine and discuss the environmental factors that may influence this. Finally, we consider the implications of regional immune specialization for inflammatory disease in the intestine.

Antigen-independent differentiation and maintenance of effector-like resident memory T cells in tissues

Differentiation and maintenance of recirculating effector memory CD8 T cells (T(EM)) depends on prolonged cognate Ag stimulation. Whether similar pathways of differentiation exist for recently identified tissue-resident effector memory T cells (T(RM)), which contribute to rapid local protection upon pathogen re-exposure, is unknown. Memory CD8αβ(+) T cells within small intestine epithelium are well-characterized examples of T(RM), and they maintain a long-lived effector-like phenotype that is highly suggestive of persistent Ag stimulation. This study sought to define the sources and requirements for prolonged Ag stimulation in programming this differentiation state, including local stimulation via cognate or cross-reactive Ags derived from pathogens, microbial flora, or dietary proteins. Contrary to expectations, we found that prolonged cognate Ag stimulation was dispensable for intestinal T(RM) ontogeny. In fact, chronic antigenic stimulation skewed differentiation away from the canonical intestinal T cell phenotype. Resident memory signatures, CD69 and CD103, were expressed in many nonlymphoid tissues including intestine, stomach, kidney, reproductive tract, pancreas, brain, heart, and salivary gland and could be driven by cytokines. Moreover, TGF-β-driven CD103 expression was required for T(RM) maintenance within intestinal epithelium in vivo. Thus, induction and maintenance of long-lived effector-like intestinal T(RM) differed from classic models of T(EM) ontogeny and were programmed through a novel location-dependent pathway that was required for the persistence of local immunological memory.

ICOS promotes IL-17 synthesis in colonic intraepithelial lymphocytes in IL-10-/- mice

In the absence of IL-10, colonic inflammation ensues, which is characterized by high levels of IL-17. Here, we demonstrate a direct correlation between ICOS expression and IL-17 production in cIELs. IL-10(-/-) mice had increased numbers of cIELs and greater colon weight. Although the CD69 early activation antigen was expressed on cIELs from normal and IL-10(-/-) mice, ICOS was expressed only on cIELs from IL-10(-/-) mice. IL-17-producing cells in IL-10(-/-) mice consisted of CD4(+) and CD8(+) cIELs; however, CD4(+) cells were the predominant IL-17-producing cell population. Culture of cIELs from IL-10(-/-) mice with IL-23 resulted in an increase in ICOS and IL-17 expression, whereas IL-10 suppressed expression of ICOS and IL-17. This occurred in primary cultures and recall stimulation experiments. The ICOS ligand B7RP-1 was up-regulated on colonic epithelial cells and on a population of large granular leukocytes during inflammation. Culture of cIELs with B7RP-1(+) DCs enhanced IL-17A production from normal cIELs but failed to do so using cIELs from ICOS(-/-) mice. In vivo treatment of IL-10(-/-) mice with antibody to ICOS resulted in a significant reduction in colonic pathology. These findings implicate ICOS as an activational signal of Th17 cells during chronic intestinal inflammation, and they suggest that under some conditions, control of ICOS expression may help to suppress chronic intestinal inflammation.

Developing an HIV cytotoxic T-lymphocyte vaccine: issues of CD8 T-cell quantity, quality and location

Issues of quantity, quality and location impact the ability of CD8 T cells to mediate protection from infection. These issues are considered in light of human immunodeficiency virus (HIV)/simian immunodeficiency virus (SIV) vaccination. Methods are reviewed that result in 100- to 1000-fold higher frequencies of vaccine-specific memory CD8 T cells than that achieved by current HIV/SIV vaccine approaches. Data demonstrating that location within mucosal tissues has a direct impact on memory CD8 T-cell function are discussed. Arguments are made that establishing memory CD8 T cells within mucosal sites of transmission, a priori to natural infection, may be essential for conferring optimal and rapid protection. Lastly, it is proposed that heterologous prime-boost vaccination with recombinant live replicating vectors, which has the potential to induce tremendous numbers of cytolytic memory CD8 T cells within mucosal tissues, would provide a far more stringent test of the hypothesis that memory CD8 T cells could, in principal, form the basis for a preventative HIV vaccine.

Sphingosine 1-phosphate dependence in the regulation of lymphocyte trafficking to the gut epithelium

It is well established that intraepithelial T lymphocytes (IELs) are derived from conventional single-positive (SP) thymocytes, as well as unconventional double-negative (DN) thymocytes and CD103⁺CD8αβ recent thymic emigrants (RTEs). We show that IELs can be divided into two groups according to their dependency on sphingosine 1-phosphate (S1P) for trafficking into the intestines. CD4 or CD8αβ naive lymphocytes originating from SP thymocytes express high levels of type 1 S1P receptor (S1P₁), and their preferential migration into the large intestine is regulated by S1P. In contrast, RTEs migrate exclusively into the small intestine, whereas DN thymic IEL precursors expressing either TCRαβ or TCRγδ migrate into both the small and large intestines. S1P does not play a role in the migration pathways of these unconventional thymic IEL precursors. Thus, down-regulation of S1P₁ expression or disruption of the S1P gradient halted conventional CD4 or CD8αβ IEL trafficking into the intestines, but did not affect the trafficking of unconventional thymic IEL precursors. These data are the first to demonstrate that a lipid-mediated system discriminates IELs originating from conventional and unconventional thymic precursors.

Intraepithelial lymphocytes: their shared and divergent immunological behaviors in the small and large intestine

At the front line of the body's immunological defense system, the gastrointestinal tract faces a large number of food-derived antigens, allergens, and nutrients, as well as commensal and pathogenic microorganisms. To maintain intestinal homeostasis, the gut immune system regulates two opposite immunological reactions: immune activation and quiescence. With their versatile immunological features, intraepithelial lymphocytes (IELs) play an important role in this regulation. IELs are mainly composed of T cells, but these T cells are immunologically distinct from peripheral T cells. Not only do IELs differ immunologically from peripheral T cells but they are also comprised of heterogeneous populations showing different phenotypes and immunological functions, as well as trafficking and developmental pathways. Though IELs in the small and large intestine share common features, they have also developed differences as they adjust to the two different environments. This review seeks to shed light on the immunological diversity of small and large intestinal IELs.

IELs: enforcing law and order in the court of the intestinal epithelium

The intestinal intraepithelial lymphocytes (IELs) are mostly T cells dispersed as single cells within the epithelial cell layer that surrounds the intestinal lumen. IELs are, therefore, strategically located at the interface between the antigen-rich outside world and the sterile core of the body. The intestine of higher vertebrates has further evolved to harbor numerous commensal bacteria that carry out important functions for the host, and while defensive immunity can effectively protect against the invasion of pathogens, similar immune reactions against food-derived antigens or harmless colonizing bacteria can result in unnecessary and sometimes damaging immune responses. Probably as a result of this unique dilemma imposed by the gut environment, multiple subsets of IEL have differentiated, which all display characteristics of 'activated yet resting' immune cells. Despite this common feature, IELs are heterogeneous with regard to their phenotype, ontogeny, and function. In this review, we discuss the different subtypes of IELs and highlight the distinct pathways they took that led to their unique differentiation into highly specialized effector memory T cells, which provide the most effective immune protection yet in a strictly regulated fashion to preserve the integrity and vital functions of the intestinal mucosal epithelium.

Striking phenotypic and functional differences in lamina propria lymphocytes from the large and small intestine of mice

Although intraepithelial T lymphocytes of the large intestine (LI) are known to differ from those of the small intestine (SI) in phenotype and function, differences in LI and SI lamina propria (LP) lymphocyte populations have not been clearly established. In this work we found striking phenotypic differences between SI and LI LP lymphocyte populations from Balb/c mice analyzed by flow cytometry. In the LI most lymphocytes were B cells and the predominant T cells were TCR-alpha beta+, CD8+. In contrast, in the SI most T lymphocytes were CD4+ expressing TCR-alpha beta+, although a higher proportion expressed TCR-gamma delta+ than in the LI. In T cells the expression of adhesion molecules and cytokines was also different between SI and LI. The proportion of LP T cells expressing alpha4beta7 and L-selectin was higher in the LI than in the SI; whereas a greater proportion of cells expressing alpha(E)beta7 were detected in the SI than in LI. Higher proportions of T cells expressing L-selectin and alpha4beta1 were detected in the intraepithelial compartment of the LI than that of the SI, whereas the number of T cells expressing alpha(E)beta7 was much higher in the SI than in the LI. The proportion of T cells spontaneously producing IL-2, IFN gamma, and IL-4 at the intraepithelial and lamina propria, in the small and large intestine, was different indicating that distinctive functional features exist in the lymphocyte populations residing at the different intestinal compartments.

T-cell activation in the curious world of the intestinal intraepithelial lymphocyte

In conventional terms, when T cells encounter appropriate stimuli, they are induced to undergo molecular and physical changes that confer upon them a state of activation. Once initiated, activation generally results in a state of full T-cell responsiveness in an all-or-none manner. Uniquely, however, the intestinal intraepithelial lymphocytes (IELs) bear features that are decidedly different from those of T cells located throughout other immunological compartments in that they exhibit some but not all properties of activated T cells, yet they can be induced to move further into activation provided appropriate costimulatory signals have been received. IEL costimulatory molecules some of which are constitutively expressed, whereas others are upregulated following T-cell receptor (TCR)/CD3 stimulation appear to hold the key to determining the nature and magnitude of the activational process. A system of activation such as this in the intestine would be expected to have great immunological protective value for the host because it would provide an untrammeled process of T-cell activation at a barrier site where the level of antigen exposure is consistently high. Clearly, however, mechanisms must be in place to insure that the IEL activation process is not inadvertently breached. These and other issues central to the operational workings of the intestinal immune system are elaborated in this article, and a model is presented in which IEL activation can be viewed as a layered, three-stage activational process.

Activation and Costimulation of Intestinal T Cells: Independent and Collaborative Involvement of CD43, OX40, and Ly-6C

T cells are present in large numbers in the epithelial lining of the small and large intestine of humans and mice. Those cells, referred to as intraepithelial lymphocytes (IELs), are critical for maintaining an effective mucosal immune response against the onslaught of enteric infectious agents and intestinal neoplasia. However, because intestinal immunity must by necessity occur rapidly and efficiently, it is concomitantly important that the local intestinal immune response be curtailed so as not to result in conditions that lead to a destructive inflammatory environment as occurs in inflammatory bowel disease (IBD). Although many aspects of the IEL activation process remain to be understood, emerging evidence indicates that costimulatory molecules on IELs are critical for activation and that they hold the key to regulating intestinal immunity across many levels. In this article, the involvement of three IEL costimulatory molecules (CD43, OX40, and Ly-6C) - working independently or in collaboration-will be discussed in the context of immunity and disease in the human and mouse intestine, and the involvement of those in sustaining the IELs in a uniquely precarious but effective state of activation readiness will be explored.

Large intestine intraepithelial lymphocytes from Apc+/+ and Apc+/Min mice and their modulation by indigestible carbohydrates: the IL-15/IL-15R alpha complex and CD4+ CD25+ T cells are the main targets

We have shown recently that some indigestible carbohydrate (short-chain fructo-oligosaccharides [sc-FOS]) reduced colon tumor incidence in Apc+/Min mice, and that this effect depended on a functional local immune system. In addition, IL-15 mRNA was concomitantly modulated in the mucosa. Since intraepithelial lymphocytes (IELs) are in close contact with intestinal epithelial cells, these cells are the candidates most likely to be involved in early cancer immunosurveillance. The present study documents the effects of sc-FOS on large intestine IELs (LI-IELs) from Apc+/+ or Apc+/Min mice by analyzing markers related to their phenotype, their activation status, and the cell surface IL-15/IL-5R alpha. In the colons of Apc+/Min mice, fewer LI-IELs expressed surface IL-15/IL-15R alpha. In addition, a lower number of CD4+ LI-IELs expressed CD25, although more LI-IELs expressed CD69, as compared to normal mice. The sc-FOS enriched diet caused a decrease in the proportion of CD25+ LI-IELs and an increase in the percentage of LI-IELs bearing surface IL-15/IL-15R alpha, independently of the Apc gene status. The IL-15/IL-15R alpha increase was, however, higher in Min mice, and returned to a level very similar to that of Apc+/+ mice when the latter mice were fed a low-fiber diet. The sc-FOS-enriched diet specifically induced an increase in CD69+ cells in Apc+/+ mice, and a decrease in the proportion of CD4+ CD25+ LI-IELs in Apc+/Min mice. Some of these modulations could contribute to the development of a better immune anticancer response in the early steps of cancer development.

The role of CD8+ cells in the establishment and maintenance of a Trichuris muris infection

Chronic infection by the caecal-dwelling intestinal murine nematode Trichuris muris occurs if given as a high-dose infection to 'susceptible' AKR mice or as a low-dose infection to the normally 'resistant' C57BL/6 mouse strain. Both regimes result in a type 1 cytokine response, i.e. high levels of IFN-gamma and IL-12. Here we show this susceptible response is associated with a large population of CD8(+) IFN-gamma(+) cells within the mesenteric lymph nodes and numerous CD8(+) cells infiltrating the caecal mucosa. Despite this, the in vivo abolition of CD8(+) cells within AKR and C57BL/6 mice, either prior to infection or once infection has become established, failed to affect chronicity, implying that CD8(+) T cells are not essential for the initiation or maintenance of the susceptible response to T. muris. Interestingly, the percentage of IFN-gamma(+) CD4(+) cells increased in treated groups, perhaps in a compensatory role. The majority of antigen-specific cytokine responses were comparable in both treated and control groups, although IL-5 was fivefold higher in animals receiving anti-CD8 mAbs and IFN-gamma was also raised in treated mice. Mastocytosis was unaltered by CD8 depletion, however, paradoxically, eosinophilia within the caecum was reduced in treated mice. Together these data clearly demonstrate that CD8(+) T cells are associated with chronic T. muris infection; however, these cells are dispensable for both the early and late phases of this response, but do appear to play a role in the regulation of certain cytokines and caecal eosinophilia.

Total parenteral nutrition-associated changes in mouse intestinal intraepithelial lymphocytes

Intraepithelial lymphocytes (IEL) play a major role in mucosal defense mechanisms against intraluminal foreign antigens. To address the role luminal nutrients have on the phenotype and function of the IEL, we administered total parenteral nutrition (TPN) to mice, with the absence of enteral intake. We hypothesized that administration of TPN would result in changes in the phenotype and function of the IEL. For this, we utilized a mouse model of TPN. A significant decline in the CD4+ IEL population occurred with TPN. Additionally, the CD8+,CD44+ IEL subset showed a 65% decline (P < 0.05), and the CD4+,CD44+ subset declined by 55% with TPN (P < 0.05). The CD8alphabeta+ population (a marker of thymic-dependence) also declined by 92% (P < 0.01) with TPN. IEL in the TPN group showed a significantly lower degree of in vitro proliferation. In conclusion, the IEL showed significant phenotypic changes with TPN including the loss of the thymic-derived population. Functionally, the IEL showed a significant decline in proliferation. Such changes demonstrate the important role luminal nutrients have on IEL phenotype and function.

Differential appearance of T cell subsets in the large and small intestine of neonatal mice

We examined the appearance of intestinal intraepithelial lymphocytes (IEL) during the first 12 wk of life to gain insight into postnatal factors that contribute to the differences found between IEL in the large and small intestines of adult mice. Intestinal T cells were very infrequent at birth, but increased in number in the large and small intestine during the first 4 wk of life and then stabilized. The small intestinal epithelium at 2 wk of age contained mostly T cell receptor (TCR) alphabeta+, CD2+ T cells, unlike IEL in adult mice, which were composed of nearly equal proportions of CD2-, TCR alphabeta+ and TCR gammadelta+ cells. Between 2 and 3 wk of age, TCR gammadelta+, CD2- IEL increased greatly in the small intestine, whereas TCR alphabeta+ cells expressing CD2 decreased. By contrast, IEL in the large intestine at 2 and 3 wk of age were mostly TCR alphabeta+, CD2+ T cells similar to large intestinal IEL in adult mice. And finally, the expression of CD69 increased earlier and to higher levels on TCR alphabeta+ and TCR gammadelta+ IEL in the small intestine than in the large intestine. Our results demonstrate that IEL in the large and small intestine are phenotypically similar during suckling and that differences between these populations are established after weaning. Furthermore, the earlier accumulation of IEL with an activated adult IEL phenotype in the small intestine suggests that these T cells mature or expand in the gut and contribute to the maturation of immune function during postnatal life in mice.

Flow cytometric analysis of colonic and small intestinal mucosal lymphocytes obtained by endoscopic biopsy in the healthy dog

Flow cytometric analysis of the lymphocyte population of the gut could provide useful information on the immune cells present in the gut that would not be easily obtained in tissue sections. However, little is known of the normal lymphocyte population in the canine gut as determined by flow cytometry, which allows for simultaneous staining of multiple cell surface antigens and identification of specific lymphocytic subsets. Therefore, intraepithelial lymphocytes were obtained from biopsies of the healthy canine proximal small intestine and colon taken with an endoscope, and flow cytometric analysis was used to characterize the lymphocyte subsets present. Endoscopic biopsy of the intestine is a minimally invasive technique commonly used for diagnostic purposes. Although CD3+ lymphocytes were the most abundant subset in both colon and small intestine, CD3+/CD8- lymphocytes predominated in the proximal small intestine, whereas CD3+/CD8+ lymphocytes did in the colon. Canine CD8+ intraepithelial lymphocytes were predominantly CD8alphabeta+ in both small intestine and colon. CD4+ intraepithelial lymphocytes were always much less numerous than CD8+ intraepithelial lymphocytes. As in man, a majority of intraepithelial lymphocytes expressed the T-cell receptor, TCRalphabeta, but TCRgammadelta was expressed by a third of intraepithelial T-cells in the proximal small intestine, and approximately 15% of those in the colon. Very few CD21+ lymphocytes were detected in samples of healthy canine colon and small intestinal intraepithelial cells. We have showed that canine intraepithelial lymphocytes are regionally specialized, and that those from the small intestine are unique in comparison to those of other species such as man and rodents due to the large numbers of CD3+/CD8- intraepithelial lymphocytes. This study provides a baseline for comparison with intraepithelial lymphocytes obtained from canine patients with intestinal disease.

Qa-2-dependent selection of CD8alpha/alpha T cell receptor alpha/beta(+) cells in murine intestinal intraepithelial lymphocytes

Murine intestinal intraepithelial lymphocytes (iIELs) are made up of a heterogeneous mix of T cells with unique phenotypes. Whereas CD8(+) T cells in peripheral lymphoid organs use CD8alpha/beta and are selected on MHC class Ia molecules, a majority of iIELs use CD8alpha/alpha. Here, we report that the presence of CD8alpha/alpha TCR-alpha/beta cells in iIELs is independent of classical MHC class I molecules K(b) and D(b), as illustrated by their presence in K(b)/D(b) double-knockout mice and in mice lacking a nonclassical MHC class I molecule, CD1d. Most strikingly, their presence is decreased by approximately 70% in mice lacking transporter associated with antigen processing (TAP). The TAP-dependent nonclassical MHC class I molecule Qa-2 is strongly implicated in the presence of these cells, as inferred from the low numbers of CD8alpha/alpha TCR-alpha/beta T cells in mice deficient in Qa-2 genes. Second, a Qa-2-transgenic mouse made in a Qa-2(-) strain showed an increase in the numbers of CD8alpha/alpha cells among its iIELs. Thus, the presence of CD8alpha/alpha TCR-alpha/beta cells in iIELs is mainly dependent on the nonclassical MHC class I molecule Qa-2.

The fermentable fiber content of the diet alters the function and composition of canine gut associated lymphoid tissue

The ingestion of plant fibers and their susceptibility to microbial fermentation in the large bowel modulate intestinal morphology but little is known about effects on the gut associated lymphoid tissue (GALT). The aim of the present study was to determine the effect of consuming diets containing different levels of fermentability fiber on immune function. Sixteen adult mongrel dogs (23 +/- 2 kg) were fed (14 days) in a randomized cross over design two isoenergetic isonitrogenous diets containing 8.3 g/kg non-fermentable or 8.7 g/kg fermentable fibers. Lymphocytes were isolated from blood prior to starting the study and at the end of each diet period. At study completion, lymphocytes were isolated from the gut associated lymphoid tissue (GALT) of the small intestine for characterization by immunofluorescence and to determine their ability to respond to mitogenic stimulation. Feeding high fermentable fibers increased (P < 0.05) the CD4/CD8 ratio and decreased (P < 0.05) the proportion of B cells in peripheral blood without changing natural killer cell activity or the response to mitogens. Mesenteric lymph node cells from dogs fed the low then high fermentable fiber diet contained a higher (P < 0.05) proportion of CD4+ cells and a higher (P < 0.05) response to mitogens. Intraepithelial, Peyer's patches and lamina propria cells contained a greater (P < 0.05) proportion of CD8+ cells when dogs were fed a low fermentable fiber diet followed by a high fermentable fiber diet. T cell mitogen responses in vitro were higher for intraepithelial but lower for Peyer's patches and lamina propria cells from dogs who were fed the low fermentable fiber diet followed by the high fermentable fiber diet (P < 0.05). In conclusion, the fermentable fiber content of the diet had very little effect on the type and function of immune cells in peripheral blood. However, feeding dogs a high fermentable fiber diet for 2 weeks (after 2 weeks of consuming a low fermentable fiber diet) altered the T-cell composition of GALT and produced a higher mitogen response in the predominantly T cell tissues and a lower response in areas involved in B cell functions. In conclusion, the level of fermentable fiber in the diet appears to alter GALT properties. Further studies are required to determine the direct contribution of a high or low fiber diet to these changes and the physiological implications to the health of the animal.

CD69 and regulation of the immune function

CD69, also known as activation inducer molecule, very early activation antigen, MLR-3 and Leu-23, is a member of the natural killer (NK) cell gene complex family of signal transducing receptors. CD69 is as a type II transmembrane glycoprotein with a C-type lectin binding domain in the extracellular portion of the molecule. CD69 expression is induced in vitro on cells of most hematopoietic lineages, including T and B lymphocytes, NK cells, murine macrophages, neutrophils and eosinophils, while it is constitutively expressed on human monocytes, platelets and epidermal Langerhans cells. Although a specific ligand for CD69 has not been identified, its wide cellular distribution and the induction of intracellular signals upon CD69 crosslinking suggest a role for the receptor in the biology of hematopoietic cells. Moreover, certain results indicate that CD69 may be involved in the pathogenesis of such diseases as rheumatoid arthritis, chronic inflammatory liver diseases, mild asthma, and acquired immunodeficiency syndrome.

High- and low-affinity single-peptide/MHC ligands have distinct effects on the development of mucosal CD8alphaalpha and CD8alphabeta T lymphocytes

In this study, we compared the influence of two peptides on the selection of CD8alphaalpha and CD8alphabeta intraepithelial lymphocytes (IELs) of the intestine, which develop by a unique and partially thymus-independent process. Mice were used in which all T cells carried one transgenic T cell antigen receptor (TCR) (F5), and in which only well defined transgenic peptides were presented by H-2Db. The first peptide, for which the F5 TCR has a high affinity, derives from the influenza virus nucleoprotein (NP68). The second peptide, NP34, is an antagonistic variant of NP68 and is recognized by the F5 TCR with low affinity. To avoid presentation of endogenous peptides or production of T cells carrying alternative TCRs, F5 TCR transgenic mice were generated that were deficient for Tap-1 and Rag-1. In these mice, no CD3(+)CD8(+) cells were found in lymph nodes, spleen, or intestine. Introduction of transgenes encoding either NP34 or NP68 along with an endoplasmic reticulum signal sequence enabled Tap-1-independent expression of each peptide in these mice. Positive selection of F5TCR+CD8(+) thymocytes was not rescued by these transgenic peptides. However, the high-affinity NP68 peptide induced maturation of CD8alphaalpha IEL, whereas the low-affinity NP34 peptide stimulated development of both CD8alphabeta and CD8alphaalpha IEL, but in smaller numbers. When both peptides were present, CD8alphabeta T cells failed to develop and the number of CD8alphaalpha IELs was lower than in mice carrying the NP68 transgene alone. These data demonstrate that single ligands with a high or low affinity for TCR are capable of inducing or inhibiting the maturation of alternative subsets of IELs.

Activation and peripheral expansion of murine T-cell receptor gamma delta intraepithelial lymphocytes

BACKGROUND & AIMS

The intestinal epithelial compartment is populated by CD8(+) alpha beta and gamma delta intraepithelial lymphocytes (IELs), which monitor the integrity of the epithelial barrier. alpha beta IELs are activated by peptide antigens presented by class I major histocompatibility complex (MHC) molecules, but it is unclear how gamma delta IELs are activated.

METHODS

G8 T-cell receptor (TCR) gamma delta transgenic (Tg) mice (specific for the class I MHC alloantigen, T22/10(b)) were crossed to class I MHC-deficient beta2-microglobulin-knockout (beta2m degrees) mice, and Tg+ IELs were examined for relative yields and surface and functional phenotype.

RESULTS

Evidence for class I MHC-induced activation of Tg+ IELs was supported by the detection of 4-fold greater numbers of Tg+ IELs in G8 x beta2m+ mice that proliferated at 15-fold higher levels than IELs from G8 x beta2m degrees mice. However, expression of CD69, production of cytokine (interleukin 2 and interferon gamma), and detection of cytolytic function for IELs in G8 x beta2m degrees mice suggested that class I MHC was not required for gamma delta IEL development or maturation.

CONCLUSIONS

These results suggest that CD8(+) TCR gamma delta IELs do not require class I MHC for development but support the notion that antigens presented by class I MHC molecules are involved in the peripheral expansion and differentiation of this subset.

Nucleosome-releasing treatment makes surviving tumor cells better targets for nucleosome-specific anticancer antibodies

Monoclonal antibody (MoAb) 2C5, a nucleosome-specific antinuclear autoantibody (ANA) from the repertoire of aged mice, was recently reported to recognize the surface of various tumor cells but not normal cells. Surface-bound nucleosomes (NSs) were previously proven to be MoAb 2C5's target on the outer membrane of tumor cells. Furthermore, MoAb 2C5 was found to have a strong antitumor effect during the early stages of tumor development. In an attempt to further increase antitumor effect of nucleosome-specific tumorocidal monoclonal antibody against established tumors, we investigated a possible way to enhance antibody association with tumor cells. Evidence is presented here demonstrating that the in vitro treatment of tumor cells (S49 T lymphoma) resulting in a partial cell death and massive liberation of intact NSs from dead tumor cells into the culture medium was accompanied by a 50-fold increase of MoAb 2C5 binding to the surface of surviving tumor cells. Massive NS release was observed in the case of S49 T-cell treatment with dexamethasone and vincristine. However, a partial cell killing that was not accompanied with NS release (EL4 lymphoma treatment with doxorubicin) did not result in the enhanced binding of MoAb 2C5 to the surface of surviving tumor cells. The use of NS-specific tumorocidal antibodies, such as MoAb 2C5, in combination with another NS release-inducing tumor therapy, should provide an enhanced antibody-tumor binding.

Generation of Intestinal Mucosal Lymphocytes in SCID Mice Reconstituted with Mature, Thymus-Derived T Cells

Transfer of peripheral lymph node lymphocytes to SCID mice leads to the long term establishment of mucosal T lymphocytes within the epithelium and lamina propria of the small and large intestines. Analysis of engrafted intraepithelial lymphocytes (IEL) showed that they had acquired a surface phenotype that in several respects is typical of IEL. In addition, the functional profile of engrafted IEL derived from lymph node T cells was similar to that of normal IEL; as the donor-derived T cells exhibited a strong cytolytic activity, a poor proliferative response to mitogenic stimuli, and a tendency to home and expand specifically in the intestine upon transfer to secondary SCID recipients. Optimal engraftment of intestinal T cells required bacterial flora, as the number of lymphocytes was greatly reduced in SCID recipients with a reduced flora. These results demonstrate that mature, thymus-derived T cells can migrate to the intestine and become functionally specialized to the intestinal milieu. The acquisition of phenotypic markers characteristic of the intestinal microenvironment by engrafted cells suggests that T cell migration of lymphocytes to the SCID intestine is not aberrant, but it may reflect processes that are ongoing in immunocompetent mice. Furthermore, these data suggest that the homing and/or expansion of typical, thymus-derived T cells in the intestine may be driven by luminal Ags such as those derived from bacterial flora.

The anatomical basis of intestinal immunity

The lymphoid tissues associated with the intestine are exposed continuously to antigen and are the largest part of the immune system. Many lymphocytes are found in organised tissues such as the Peyer's patches and mesenteric lymph nodes, as well as scattered throughout the lamina propria and epithelium of the mucosa itself. These lymphocyte populations have several unusual characteristics and the intestinal immune system is functionally and anatomically distinct from other, peripheral compartments of the immune system. This review explores the anatomical and molecular basis of these differences, with particular emphasis on the factors which determine how the intestinal lymphoid tissues discriminate between harmful pathogens and antigens which are beneficial, such as food proteins or commensal bacteria. These latter antigens normally provoke immunological tolerance, and inappropriate responses to them are responsible for immunopathologies such as food hypersensitivity and inflammatory bowel disease. We describe how interactions between local immune cells, epithelial tissues and antigen-presenting cells may be critical for the induction of tolerance and the expression of active mucosal immunity. In addition, the possibility that the intestine may act as an extrathymic site for T-cell differentiation is discussed. Finally, we propose that, under physiological conditions, immune responses to food antigens and commensal bacteria are prevented by common regulatory mechanisms, in which transforming growth factor beta plays a critical role.

Beta2 integrins and ICAM-1 are involved in establishment of the intestinal mucosal T cell compartment

Development of the mucosal immune system was examined in mice with partial loss of expression of ICAM-1 or CD18. Profound effects on Peyer's patch (PP), lamina propria (LP), and intraepithelial lymphocyte (IEL) T cell populations were observed in mutant mice. Normal expression of CD18 integrins and ICAM-1 was essential for development of the CD8(alpha beta) TCR(alpha beta)LP and IEL compartment and for the generation of normal PP lymphocyte populations. The partial loss of CD8(alpha beta) IEL correlated with the loss of TCR(alpha beta) IEL-mediated lytic activity. The presence of a subset of Thy1+TCR(gamma delta)IEL was also dependent on CD18 integrins and ICAM-1. Both the lytic activity and the expression of CD11c by TCR(gamma delta)IEL were up-regulated in the presence of TCR(alpha beta) T cells. Analysis of bone marrow chimeras demonstrated that a bone marrow-derived ICAM-1+ accessory cell was involved in the generation of some TCR(alpha beta) IEL. These results demonstrated that ICAM-1 and beta2 integrins were required for establishment of a normal intestinal immune system.

Polyclonal expansion of adoptively transferred CD4+ alpha beta T cells in the colonic lamina propria of scid mice with colitis

The adoptive transfer of low numbers of peripheral, non-fractionated CD4+ alpha beta T cells into histocompatible, severely immunodeficient (scid) hosts induces a colitis. This disease developed in C.B-17 scid/scid hosts after the injection of 10(5) CD4+ T cells purified from different peripheral lymphoid organs of immunocompetent C.B.-17 +/+ or BALB/cdm2 donor mice. Irrespective of their tissue origin, transferred CD4+ T cells selectively repopulated the scid host with gut-seeking CD4+ T cells. A chronic inflammatory bowel disease (IBD) developed as polyclonal populations of mucosa-seeking memory/effector CD4+ T cells accumulated in the gut lamina propria and epithelial layer of the adoptive host. The manifestation of colitis in the scid host correlated with the in situ polyclonal activation and expansion of adoptively transferred CD4+ T cells in the colonic lamina propria. Attempts were unsuccessful to select in vivo an oligoclonal CD4+ T cell population with an enhanced IBD-inducing potential by repeatedly reinjecting 10(5) donor-type CD4+ T cells from the colonic lamina propria of transplanted scid mice with an early and severe IBD into new scid hosts. The data indicate that the preferential repopulation of gut-associated lymphoid tissues with immunocompetent CD4+ T cells, and their polyclonal activation and in situ expansion in the lamina propria of the histocompatible, immunodeficient host are critical events in the pathogenesis of an IBD in this model.

Intraepithelial lymphocytes in colon have similar properties to intraepithelial lymphocytes in small intestine and hepatic intermediate TCR cells

Recently, properties of intraepithelial lymphocytes (IEL) in the colon (C-IEL) have been analyzed in comparison with those of IEL in the small intestine (SI-IEL). We compared the properties of C-IEL with those of SI-IEL and hepatic intermediate TCR cells, two other types of extrathymic T cells. C-IEL and intermediate TCR cells contain many NK1+T cells, although SI-IEL contain few. V gamma and V delta usage of C-IEL was the same as that SI-IEL, and that of intermediate TCR cells was different. C-IEL responded to Con A while SI-IEL did not. As to adhesion molecules, C-IEL include both extrathymic and thymus-originated type T cells. With age, TCR- alpha beta(+) CD4+ CD8+ cells do not increase among C-IEL but do increase among SI-IEL. IL-2R beta(+) or CD4- CD8- C-IEL increase as observed in the liver. These results indicate that these organ-specific T cells have different roles at their respective sites and that they may be of different lineages.

Co-expression of CD8 alpha in CD4+ T cell receptor alpha beta + T cells migrating into the murine small intestine epithelial layer

We investigated the surface phenotype of CD3+CD4+ T cell receptor (TCR) alpha beta + T cells repopulating the intestinal lymphoid tissues of C.B-17 scid/scid (severe-combined immunodeficient; scid) (H-2d, Ld+) mice. CD4+ CD8- T cells were cell sorter-purified from various secondary and tertiary lymphoid organs of congenic C.B-17 +/+ (H-2d, Ld+) or semi-syngeneic dm2 (H-2d, Ld-) immunocompetent donor mice. After transfer of 10(5) cells into young scid mice, a mucosa-homing, memory CD44hi CD45RBlo CD4+ T cell population was selectively engrafted. Large numbers of single-positive (SP) CD3+ CD2+ CD28+ CD4+ CD8- T cells that expressed the alpha 4 integrin chain CD49d were found in the spleen, the mesenteric lymph nodes, the peritoneal cavity and the gut lamina propria of transplanted scid mice. Unexpectedly, large populations of donor-type double-positive (DP) CD4+ CD8 alpha + CD8 beta - T cells with high expression of the CD3/TCR complex appeared in the epithelial layer of the small intestine of transplanted scid mice. In contrast to SP CD4+ T cells, the intraepithelial DP T cells showed low expression of the CD2 and the CD28 co-stimulator molecules, and of the alpha 4 integrin chain CD49d, but expressed high levels of the alpha IEL integrin chain CD103. The TCR-V beta repertoire of DP but not SP intraepithelial CD4+ T cells was biased towards usage of the V beta 6 and V beta 8 viable domains. Highly purified populations of SP and DP CD4+ T cell populations from the small intestine epithelial layer of transplanted scid mice had different abilities to repopulate secondary scid recipient mice: SP CD4+ T cells repopulated various lymphoid tissues of the immunodeficient host, while intraepithelial DP CD4+ T cells did not. Hence, a subset of CD3+ CD4+ TCR alpha beta + T cells apparently undergoes striking phenotypic changes when it enters the microenvironment of the small intestine epithelial layer.

Extrathymic T cell differentiation

In the mouse, the gut mucosa is a major site of extrathymic differentiation of T cells. Recent data in this past year show that this process differs from the main thymic differentiation pathway not only in its location, but also in its use of costimulatory molecules, signal transduction modules, and mechanisms of repertoire selection. The thymus exerts an influence on the expansion of the extrathymically differentiated gut intraepithelial lymphocytes that appears to be varied in nature, including acting as a source of TCR- progenitors. All gut intraepithelial lymphocytes, whatever their extrathymic or thymic site of differentiation, have common features of activated and specialized cytotoxic cells. Other T cells may differentiate extrathymically, in particular in the liver; these later cells appear to have a very restricted, probably autoreactive repertoire, and also display natural killer cell features.