Rational application of targeted therapeutics in mucinous colon/appendix cancers with positive predictive factors

Molecular‐targeted therapies have demonstrated disappointing results against most advanced solid cancers. This may largey be attributed to irrational drug use against unselected cancers. We investigated the efficacy of dual MEK‐PI3K drug therapy against KRAS mutated mucin 2 (MUC2)‐secreting LS174T cells and patient‐derived ex vivo and in vivo models of KRAS mutated mucinous colon/appendix cancers. These tumors demonstrate unique phenotypic and genotypic features that likely predict sensitivity to this targeted co‐therapy. Co‐treatment with MEK inhibitor (trametinib) and PI3K inhibitor (pictilisib)‐induced synergistic cytotoxicity and intrinsic mitochondrial‐mediated apoptosis in LS174T cells and tumor explants in vitro. Dual drug therapy also induced endoplasmic reticulum stress (ERS)‐associated proteins (GRP78/BiP, ATF4, and CHOP). However, CHOP knock‐down assays demonstrated that mitochondrial‐mediated apoptosis in LS174T cells was not ERS‐dependent. Dual drug therapy also significantly decreased MUC2 expression, MUC2 post‐translational modification (palmitoylation) and secretion in LS174T cells, suggesting a simultaneous cytotoxic and mucin suppressive mechanism of action. We also demonstrated effective mucinous tumor growth suppression in ex vivo epithelial organoid (colonoid) cultures and in in vivo intraperitoneal patient‐derived xenograft models derived from mucinous colon/appendix cancer. These promising preclinical data support a role for dual MEK‐PI3K inhibitor therapy in mucinous colon/appendix cancers. We postulate that mucinous KRAS mutated cancers are especially vulnerable to this co‐treatment based on their unique phenotypic and genotypic characteristics.

[Structure and cytoarchitectonic of the lymphoid tissue of the Appendix of man in elderly and senile ages.]

In recent years in many countries with increasing duration of human life, there is an aging population. In this regard, studies of lymphoid tissue that provides immune processes in the human body, are of particular relevance. It was studied lymphoid tissue of the Appendix person aged 54-81 and 26-35 years with histological and statistical methods. In the older age groups there was a reduction and restructuring of lymphoid tissue with partial modified lymphoid nodules. Most nodules have no light centers to continue the process of blast transformation. In the central zones of the nodules with light center observed mitoses. There is an active migration of the lymphocytes in the lymphatic channel. The condition of the lymphoid tissue of the appendix depends on the individual characteristics of the human body. In some cases, people of advanced age are noted for its complete reduction and closure of the lumen of the organ.

The appendix as a viable source of neural progenitor cells to functionally innervate bioengineered gastrointestinal smooth muscle tissues

Appendix-derived neural progenitor cells (NPCs) have both neurogenic and gliogenic potential, but use of these cells for enteric neural cell therapy has not been addressed. The objective of this study was to determine whether NPCs obtained from the appendix would differentiate into enteric neural subsets capable of inducing neurotransmitter-mediated smooth muscle cell (SMC) contraction and relaxation. NPCs were isolated from the appendix and small intestine (SI) of rabbits. Bioengineered internal anal sphincter constructs were developed using the same source of smooth muscle and innervated with NPCs derived from either the appendix or SI. Innervated constructs were assessed for neuronal differentiation markers through Western blots and immunohistochemistry, and functionality was assessed through force-generation studies. Expression of neural and glial differentiation markers was observed in constructs containing appendix- and SI-derived NPCs. The addition of acetylcholine to both appendix and SI constructs caused a robust contraction that was decreased by pretreatment with the neural inhibitor tetrodotoxin (TTX). Electrical field stimulation caused relaxation of constructs that was completely abolished in the presence of TTX and significantly reduced on pretreatment with nitric oxide synthase inhibitor (Nω-nitro-l-arginine methyl ester hydrochloride [l-NAME]). These data indicate that in the presence of identical soluble factors arising from intestinal SMCs, enteric NPCs derived from the appendix and SI differentiate in a similar manner and are capable of responding to physiological stimuli. This coculture paradigm could be used to explore the nature of the soluble factors derived from SMCs and NPCs in generating specific functional innervations.

SIGNIFICANCE

This study demonstrates the ability of neural stem cells isolated from the appendix to differentiate into mature functional enteric neurons. The differentiation of neural stem cells from the appendix is similar to differentiation of neural stem cells derived from the gastrointestinal tract. The appendix is a vestigial organ that can be removed with minimal clinical consequence through laparoscopy. Results presented in this paper indicate that the appendix is a potential source of autologous neural stem cells required for cell therapy for the gastrointestinal tract.

Isolation of mesenchymal stem cells from human vermiform appendix

BACKGROUND

Recent findings have shown that pluripotent stem cells exist in areas outside the bone marrow (BM). Moreover, it has been demonstrated that the appendix is important for the development of mucosal gut immunity, and hematopoietic progenitors have been isolated from animal and human appendices.

MATERIALS AND METHODS

Non-inflamed appendices removed during laparotomy were processed and cultured until the appearance of adherent cells. Differentiations (performed under osteogenic, adipogenic, and myogenic conditions) were confirmed by immunohistochemistry and cytochemistry. Polymerase chain reaction and cytofluorimetric analyses were performed to evidence the presence of genes and protein specific lineages in appendix-derived mesenchymal stem cells (ADMCs).

RESULTS

ADMCs were present in non-inflamed appendices. ADMCs under osteogenic conditions differentiated in osteoblasts and showed increased alkaline phosphatase expression; at the gene level, we observed the expression of Core binding factor alpha 1 (Cbfa1) and osteocalcin in osteogenic induced ADMCs. Under adipogenic conditions, lipidic drops in the cytoplasm, expression of lipoprotein lipase (LpL), and peroxisome proliferator-activated receptor gamma were observed; under myogenic conditions, myotubes expressing muscle specific proteins like desmin were formed. Myogenic regulatory factor 4 and MyoD were selectively induced in the ADMCs under myogenic conditions.

CONCLUSIONS

This study shows for the first time that mesenchymal stem cells can be isolated from normal appendices obtained from a pediatric and adult age group (0-18 years of age). This finding not only may further knowledge of the maturation of the intestinal immunesystem but also could indicate a new physiological role of the human vermiform appendix.

Mast cells in surgically resected appendices

Mast cells are known to be effector cells in various inflammatory reactions, but their role in appendicitis is unclear. The present study was undertaken to investigate the extent of mast cell involvement in appendicitis and evaluate their possible role. A total of 150 appendices including normal and inflamed appendices, were assessed for their histological changes and density of neutrophil, lymphocyte and eosinophil infiltration. The mast cells were counted in 1% toluidine blue-stained sections. It was found that eosinophil counts in all the layers were significantly low in normal appendices (P<0.01) and in chronic appendicitis (P<0.1) as compared to acute appendicitis. Mast cell counts were lowest in normal appendices, significantly higher in acute appendicitis (P<0.01) and highest in chronic appendicitis (P<0.001). Obstruction due to faecoliths or parasites were seen in only 20.1% and 2.1% of the inflamed appendices respectively. Hence a Type I hypersensitivity reaction with release of mediators by mast cells might be another triggering factor for the sequence of events leading to appendicitis.

CD5+ B cells are preferentially expanded in rabbit appendix: the role of CD5 in B cell development and selection

Although only a small proportion of mouse and human B cells are CD5(+), most adult rabbit B cells express CD5. However, CD5 was not detectable on the majority of B cells in neonatal appendix 1 and 3days after birth. Cell trafficking studies demonstrated that CD5(+) and CD5(-) CD62L(+) B cells from bone marrow migrated into appendix. There, CD5(+) B cells were preferentially expanded and predominated by approximately 2weeks of age. In mutant ali/ali rabbits, VHa2(+) B cells develop through gene conversion-like alteration of rearranged VH genes upstream of deleted VH1a2. Correlated appearance of individual CD5(+) germinal centers and VHa2(+) B-cells in mutant appendix suggests that CD5 binding positively selects cells with a2(+) framework regions that bind CD5. Following negative and positive selection, cells with diversified rearranged heavy- and light-chain sequences exit appendix, migrate to peripheral tissues and constitute the preimmune repertoire of CD5(+) B cells that encounter foreign antigens.

Increased expression of soluble decoy receptor 3 in acutely inflamed intestinal epithelia

Decoy receptor 3 (DcR3), a soluble receptor in the tumor necrosis factor (TNF) receptor family, is known to inhibit apoptosis mediated by pro-apoptotic TNF family cytokines such as Fas ligand (FasL), TL1A, and LIGHT. Therefore, the regulation of DcR3 expression under certain pathophysiological conditions is of interest since the level of soluble DcR3 would most likely affect the homeostasis of cells and tissues. We found that human intestinal epithelial cell (IEC) lines (SW480, SW620, and HT29) could selectively increase DcR3 release in response to lipopolysaccharide (LPS) and that all the cells preferentially expressed Toll-like receptor 4 (TLR-4). LPS-induced DcR3 releases in IECs appeared to be via the activation of mitogen-activated protein kinases (MAPK) such as extracellular signal-regulated kinase 1 and 2 (ERK1/2) and c-Jun NH2-terminal protein kinase (JNK), and the transcription factor NF-kappaB. Moreover, the increased expression of DcR3 in appendix epithelia from patients with acute appendicitis was demonstrated. Taken together, the results indicated that DcR3 might play an important role in the human intestinal epithelium during acute inflammatory processes caused by endotoxin challenge.

Interaction of pathogenic bacteria with rabbit appendix M cells: bacterial motility is a key feature in vivo

Rabbit appendix consists mainly of lymphoid follicles (LF) covered by M cells, the specialized antigen-sampling cells of the mucosal immune system, and surrounded by glandular epithelium. Until now, these M cells have been characterized morphologically and histologically by using cellular markers. Here, the adhesion and transport of pathogenic bacteria were investigated to assess the function of M cells of the appendix. We used the enteroinvasive motile Salmonella typhimurium and the rabbit enteropathogenic non-motile Escherichia coli RDEC-1, which are known to target specifically rabbit M cells of Peyer's patches (PPs). We found that S. typhimurium efficiently attached and was transported through appendix M cells in vivo. In contrast to S. typhimurium, RDEC-1 targeted M cells only ex vivo, when bacteria were allowed to have direct contact with the surface of the follicle. The difference in interaction of the two bacteria with appendix M cells led us to investigate whether this could be correlated with the lack of motility of RDEC-1. We used an aflagellate mutant of S. typhimurium and found that it had the same infection phenotype as RDEC-1. Gene complementation restored the efficiency of infection to that of S. typhimurium wild-type strain. In conclusion, we show that M cells of the appendix display features of the canonical M cells of PP, since they efficiently sample luminal pathogenic bacteria. However, due to the morphology of the appendix, motile bacteria appear to be more potent in their interactions with appendix M cells.

Analysis of mutational lineage trees from sites of primary and secondary Ig gene diversification in rabbits and chickens

Lineage trees of mutated rearranged Ig V region sequences in B lymphocyte clones often serve to qualitatively illustrate claims concerning the dynamics of affinity maturation. In this study, we use a novel method for analyzing lineage tree shapes, using terms from graph theory to quantify the differences between primary and secondary diversification in rabbits and chickens. In these species, Ig gene diversification starts with rearrangement of a single (in chicken) or a few (in rabbit) V(H) genes. Somatic hypermutation and gene conversion contribute to primary diversification in appendix of young rabbits or in bursa of Fabricius of embryonic and young chickens and to secondary diversification during immune responses in germinal centers (GCs). We find that, at least in rabbits, primary diversification appears to occur at a constant rate in the appendix, and the type of Ag-specific selection seen in splenic GCs is absent. This supports the view that a primary repertoire is being generated within the expanding clonally related B cells in appendix of young rabbits and emphasizes the important role that gut-associated lymphoid tissues may play in early development of mammalian immune repertoires. Additionally, the data indicate a higher rate of hypermutation in rabbit and chicken GCs, such that the balance between hypermutation and selection tends more toward mutation and less toward selection in rabbit and chicken compared with murine GCs.

Developing neonatal rabbit appendix, a primary lymphoid organ, is seeded by immature blood-borne B cells: evidence for roles for CD62L/PNAd, CCR7/CCL21, alpha4beta1 and LFA-1

Young rabbit appendix is a homologue of chicken bursa of Fabricius; both are crucial sites for preimmune B-cell repertoire development. We describe here some of the molecules involved in the multi-step recruitment of blood-borne B cells into neonatal rabbit developing appendix. Sialyl-Lewis-x, CD62L and integrins such as LFA-1 and alpha4beta1 were detected on B cells in peripheral blood. Peripheral lymph node addressin (PNAd), a CD62L counter-receptor was observed on appendix HEV. We also detected chemokine receptor CCR7 on peripheral blood B cells and one of the CCR7 ligands, CCL21, on appendix HEV but not in appendix follicles. Higher levels of CXCR5 expression compared to CCR7 on appendix B cells suggest that CXCR5 may be involved in recruitment of B cells into follicles. The proportions of appendix B cells expressing CD62L, sialyl-Lewis-x and alpha4beta1 declined between day 3 and 4 weeks after birth while percentages of Lewis-x+ appendix B cells increased. These changes correlate with the stage of repertoire diversification by gene conversion in both rabbits and chickens. The cross-reactivity of antibodies to mouse or human adhesion molecules described in this study indicates that some of the structures of these important molecules are conserved across species.

Role of commensal bacteria in development of gut-associated lymphoid tissues and preimmune antibody repertoire

Intestinal bacteria are required for development of gut-associated lymphoid tissues (GALT), which mediate a variety of host immune functions, such as mucosal immunity and oral tolerance. In rabbits, the intestinal microflora are also required for developing the preimmune Ab repertoire by promoting somatic diversification of Ig genes in B cells that have migrated to GALT. We studied the mechanism of bacteria-induced GALT development. Bacteria were introduced into rabbits in which the appendix had been rendered germfree by microsurgery (we refer to these rabbits as germfree-appendix rabbits). We then identified specific members of the intestinal flora that promote GALT development. The combination of Bacteroides fragilis and Bacillus subtilis consistently promoted GALT development and led to development of the preimmune Ab repertoire, as shown by an increase in somatic diversification of VDJ-C micro genes in appendix B cells. Neither species alone consistently induced GALT development, nor did Clostridium subterminale, Escherichia coli, or Staphylococcus epidermidis. B. fragilis, which by itself is immunogenic, did not promote GALT development; hence, GALT development in rabbits does not appear to be the result of an Ag-specific immune response. To identify bacterial pathways required for GALT development, we introduced B. fragilis along with stress-response mutants of B. subtilis into germfree-appendix rabbits. We identified two Spo0A-controlled stress responses, sporulation and secretion of the protein YqxM, which are required for GALT development. We conclude that specific members of the commensal, intestinal flora drive GALT development through a specific subset of stress responses.

[Histotopography of colon endocrine cells in the mucosal epithelium of some mammals and in man]

Histotopography of colon endocrine cells in the mucosal epithelium of adult rabbits, white rats and man was studied by light microscopy. The number of endocrinocytes in rabbit and human colon was seen to increase towards the rectum, which reflects a general tendency in mammals. In the appendices of the investigated subjects, essential distinctions in endocrine cell contents were revealed. So, in rabbits, the maximum quantity of endocrine cells (135 +/- 15 cell/mm2) was observed in the appendix if compared to other parts of the colon (except rectum), whereas in the human appendix, the number of endocrine cells is minimal (13 +/- 3 cell/mm2). In all parts of rabbit and rat caeca endocrine cell contents are similar to those in the nearby part of the colon, which suggested that according to the given parameter the caecum shows no specifity.

Structure, lymphatic vascularization and lymphocyte migration in mucosa-associated lymphoid tissue

In this review, we consider the morphological aspects and topographical arrangement of gut-associated lymphoid tissue (GALT) (solitary and aggregate lymph nodules or Peyer's patches) and of vermiform appendix in the human child and in some mammals. The spatial arrangement of the vessels belonging to apparatus lymphaticus periphericus absorbens (ALPA) and of blood vessels within each lymphoid follicle as well as the ultrastructural characteristics of the lymphatic endothelium with high absorption capacity are considered. Particular attention is also paid to the morphological and biomolecular mechanisms inducing lymphocyte transendothelial migration to the bloodstream by means of lymphatic vessels as well as their passage from blood into lymphoid tissue through the high endothelial venules (HEVs). The preferential transendothelial passage of lymphocytes and polymorphonuclear neutrophils within ALPA vessels of the interfollicular area does not occur following the opening of intercellular contacts, but rather it occurs by means of 'intraendothelial channels'. In HEVs, on the contrary, the hypothesis is plausible that lymphocyte transendothelial migration into lymphoid tissue occurs through a channel-shaped endothelial invagination entirely independent of interendothelial contacts. The lymph of ALPA vessels of the single Peyer's patch is conveyed into precollector lymphatic vessels and into prelymph nodal collectors, totally independent of the ALPA vessels of the gut segments devoid of lymphoid tissue. The quantitative distribution of T lymphocytes in the lymph of mucosal ALPA vessels suggests a prevalent function of fluid uptake, whereas a reservoir and supply function is implicated for the vessels of interfollicular area. The precollector lymphatic vessels and prelymph nodal collectors are considered to be vessels with low absorption capacity, whose main function is lymph conduction and flow.

Prepro-endothelin-1 mRNA and its mature peptide in human appendix

Because the precise immunopathological events occurring in appendicitis are not completely understood, possible local production of endothelin-1 (ET-1) in human appendix was investigated. We used immunohistochemistry and in situ hybridization to detect the presence, distribution, and phenotype of ET-1-positive cells and prepro-ET-1 (pp-ET-1) mRNA-expressing cells. ET-1-positive stromal cells and pp-ET-1 mRNA-expressing cells were detected with different distributions and relative frequencies in normal control appendix, histologically normal appendix, and inflamed appendix. Six of 20 histologically normal appendixes from patients with a clinical diagnosis of acute appendicitis had many ET-1-positive stromal cells and high pp-ET-1 mRNA expression, similar to inflamed appendix. Forty percent of the pp-ET-1 mRNA-expressing cells were neutrophils, and the other positive cells were mast cells and macrophages. We suggest that local production of ET-1 by neutrophils and other inflammatory cells could be a molecular sign of focal inflammation in histologically normal appendixes and that ET-1 could be implicated, with other cytokines, in the pathogenesis of appendicitis by inducing appendiceal ischemia through vasoconstriction.

Histology of vermiform appendix-like organ in slow loris

The vermiform appendix-like organ (VALO) of the slow loris was investigated for its histology and immunohistochemical characteristics. The VALO has a much thinner wall with flat folded mucosa and shallower crypts than the cecal mucosa, while cellular components and population of the mucosa were similar to those of the cecum. No coalescent lymph nodules were seen in the submucosa. Immunohistochemically 5-HT-positive cells in the crypts and CD3- and CD8-positive lymphocytes in the lymph nodules were shown in the VALO as well as in the cecum. These findings suggest that the VALO is a low-differentiated vermiform appendix of the slow loris.

Neutrophil count in the normal appendix and early appendicitis: diagnostic index of real acute inflammation

It is generally accepted that the uninflammed appendix does not contain neutrophils. In view of that, we searched for the presence of neutrophils in 60 uninflammed appendectomies and compared the findings with the neutrophil count in 20 cases of early appendicitis. In the uninflammed appendix, the upper third of the mucosa showed a mean of 0.75 neutrophils (N) per 5 high power fields (HPF), 4.71 N/5 HPF in the middle third, and 2.70 N/5 HPF in the deep third. At the suberosa, a mean of 3.41 and 3.32 N per 10 post-capillary venules in respectively longitudinal and transverse sections of the organ were present. The number of neutrophils in the mucosa showed a positive correlation with the number in the subserosa. In the early appendicitis we observed a mean of 12.53 N/5 HPF in the upper third, 11.33 N/5 HPF in the middle third, and 13.0 N/5 HPF in the deep third; at the subserosa, a mean of 4.95 N/10 post-capillary venules in transverse sections and 4.45 N/10 post-capillary venules in longitudinal sections was observed. No positive correlation between N in the mucosa and subserosa was observed. The count of N in the mucosa of normal appendix and early appendicitis showed a significant difference (P <.005). We conclude that, although present, not more than 10 neutrophils/5 HPF are found in the mucosa of uninflammed appendixes. Neutrophil count in the lamina propria should support the diagnosis of "normal" appendix and could be an indicator for suspecting early appendicitis, preventing underdiagnosis.

Cloning and characterization of human Siglec-11. A recently evolved signaling molecule that can interact with SHP-1 and SHP-2 and is expressed by tissue macrophages, including brain microglia

Siglecs are sialic acid-recognizing animal lectins of the immunoglobulin superfamily. We have cloned and characterized a novel human molecule, Siglec-11, that belongs to the subgroup of CD33/Siglec-3-related Siglecs. As with others in this subgroup, the cytosolic domain of Siglec-11 is phosphorylated at tyrosine residue(s) upon pervanadate treatment of cells and then recruits the protein-tyrosine phosphatases SHP-1 and SHP-2. However, Siglec-11 has several novel features relative to the other CD33/Siglec-3-related Siglecs. First, it binds specifically to alpha2-8-linked sialic acids. Second, unlike other CD33/Siglec-3-related Siglecs, Siglec-11 was not found on peripheral blood leukocytes. Instead, we observed its expression on macrophages in various tissues, such as liver Kupffer cells. Third, it was also expressed on brain microglia, thus becoming the second Siglec to be found in the nervous system. Fourth, whereas the Siglec-11 gene is on human chromosome 19, it lies outside the previously described CD33/Siglec-3-related Siglec cluster on this chromosome. Fifth, analyses of genome data bases indicate that Siglec-11 has no mouse ortholog and that it is likely to be the last canonical human Siglec to be reported. Finally, although Siglec-11 shows marked sequence similarity to human Siglec-10 in its extracellular domain, the cytosolic tail appears only distantly related. Analysis of genomic regions surrounding the Siglec-11 gene suggests that it is actually a chimeric molecule that arose from relatively recent gene duplication and recombination events, involving the extracellular domain of a closely related ancestral Siglec gene (which subsequently became a pseudogene) and a transmembrane and cytosolic tail derived from another ancestral Siglec.

[Morphological characteristics of glands of the ileocecal angle sphincter region in adults]

Structural feature of the large intestine glands (Liberkun crypts), located in the thickness of the ileocoecal angle valve and in the zone of appendix valve were studied using macro-microscopic methods. The material was obtained from cadaveres of 28 men and women who died at the age of 60-67. The causes of their deaths were not associated with digestive or immune system pathology. Morphometric investigations performed revealed that the density of the glands arrangement in these sphincter zones of the large intestine ileocecal angle, the area occupied by them and their length both on cross and longitudinal sections exceeded the same parameters in the zone of the coecum cone in all the observations.

Rabbit M cells and dome enterocytes are distinct cell lineages

We have studied the M cell origin and differentiation pathway in rabbit gut-associated lymphoid tissues. Micro-dissected domes and epithelium isolated by ethylene diamine tetra acetic acid detachment allowed us to view the whole epithelial surface from the bottom of crypts to the top of domes. We used monoclonal antibodies specific to the apex of either M cells or dome enterocytes, lectins, and antibodies to vimentin in appendix, distal Peyer’s patches and caecal patches.

The earliest vimentin-labeled M cells were observed in the BrdU-positive proliferative zone of dome-associated crypts. Gradual differentiation of the M cell vimentin cytoskeleton started at this site to progressively give rise to the first pocket-forming M cells in the upper dome. Therefore, these mitotic cells of the crypts appear as the direct precursors of M cells. In addition to an early appearance of M cell markers, a regular mosaic-like relative distribution of M cells and dome enterocytes was already detected in the vicinity of crypts, similar to that observed on the lateral surface of domes where functional M cells lie. This constant distribution implies that there is no trans-differentiation of enterocytes to M cells along the crypt-dome axis. Together, these observations provide very strong evidence in favor of an early commitment in crypts of M cell and enterocyte distinct lineages.

Ulcerative colitis of the appendix ('ulcerative appendicitis') mimicking acute appendicitis

Appendiceal involvement in ulcerative colitis may occur in the setting of either diffuse or distal disease, and is usually diagnosed incidentally at the time of proctocolectomy. The present patient had a rare case of 'ulcerative appendicitis' occurring on a background of clinically quiescent ulcerative colitis, and presented with the signs and symptoms of acute appendicitis.

Histological features of resolving acute, non-complicated phlegmonous appendicitis

The histological features of resolving acute appendicitis are described. Formalin-fixed, paraffin-embedded appendices of 200 cases with acute, non-complicated phlegmonous appendicitis were reviewed. In 80 out of 200 cases, a histological picture characterized by a predominantly lymphocytic infiltrate of the subserosa and muscularis propria or the subserosa alone was found. In the affected muscularis propria, eosinophils were admixed with lymphocytes, and the cellular infiltrate showed a lesser degree than that of the classic phlegmonous appendicitis. A multifocal, rather than a diffuse pattern of infiltration was observed. Cases were divided into three groups. Group 1: appendices with the typical features of phlegmonous appendicitis: 120 cases, 60%. Group 2: appendices with a predominantly lymphocytic infiltrate in the muscularis propria, subserosa, or both, and no granulation tissue: 65 cases, 32.5%. Group 3: appendices with granulation tissue: 15 cases, 7.5%. Complicated appendicitis was excluded. Data on the duration of the clinical symptoms were derived from the clinical history. The differences between the mean duration time of groups 1 and 2, and of groups 2 and 3 were statistically significant. The findings support the contention that a mixed infiltrate of lymphocytes and eosinophils represents a regression phase of acute appendicitis.

[Intraepithelial enteroendocrine cells in cecum and appendix from ovoalbumin sensitized rabbits]

Intraepithelial enteroendocrine cells (IEC) produce peptides which influence motility, secretion and absorption of nutrients. Recently the role of these cells in the immune mucosal system is under study. The aim of the present study was to evaluate the modifications in number of IEC in cecum and appendix from Ovalbumin (OVA) sensitized rabbits. Twenty adult New Zealand rabbits were separated in two groups: Group 1 (G1 = 10) not sensitized normal control. Group 2 (G2 = 10) were sensitized twice intraperitoneally with 70 mg OVA and 30 mg ALUM/ml (aluminium hydroxide). Anti OVA specific IgE was evaluated by means of PCA test (passive cutaneous anaphylaxis). Samples form cecum and appendix were fixed in buffered formaldehyde 10%, paraffin embedded and stained with anti-Chromogranin A for neuroendocrine cells. 400 high power fields were counted in each animal, referred as IEC/100 enterocytes. In cecum surface epithelium and crypt were considered. Surface epithelium, deep crypts and superficial crypts were evaluated in appendix. Results showed in cecum in G1:1,6 IEC/100 enterocytes in surface epithelium and 3/100 in crypts; G2 6 IEC/100 in surface epithelium and 12/100 in crypts. The difference between G1 and G2 was statistically significant (p < 0.05). In appendix surface epithelium from G1 showed 5.2/100 while G2 5.4/100. Superficial crypts 8.5 (G1) and 11.3 (G2) (p < 0.05) and deep crypts 4.9 (G1) and 8.5 (G2) (p < 0.01). The results showed that OVA-sensitized animals presented increment in the number of IEC in surface epithelium and crypts which may indicate a relationship between these cells and rabbit mucosal immune system.

Phenotypic pattern of B cells in the appendix: reduced intensity of CD19 expression

The lymphoid tissue of the appendix is considered as part of the gut-associated lymphoid tissue (GALT). In order to understand better the immunological significance of the appendix we analyzed the cellular composition of normal and inflamed human appendix tissue by flow cytometer with special attention to expression of the CD19 and CD5 markers on B cells. Cellular analysis was also performed on peripheral and appendical vein blood samples as well as on omentum and peritoneal fluid samples. The study population included seventeen patients aged 2-15 yr. (mean age - 11.5 yr.) undergoing appendectomy. Ten children were diagnosed with acute appendicitis while 7 had a normal appendix.

RESULTS

Compared to the peripheral blood, the appendix contained a significantly higher percentage of CD19 cells (47.6% of total lymphocytes versus 15%, p<0.0001), and B1 cells (4.98% of total lymphocytes versus 2.42%, p=0.001). In addition, the intensity of CD19-staining was markedly decreased in the appendix (mean - 395.7), and also in the omentum (mean - 398.2) as compared to peripheral lymphocytes (mean - 497.7, p<0.0001 for both comparison). Comparison between the inflamed and the non-inflamed appendices revealed that the inflamed appendix contained a significantly higher proportion of B1 cells (5.64% of total lymphocytes versus 3.53%, p=0.032), and also a higher B1/b cell ratio (0.13 vs. 0.07, p=0.01).

CONCLUSIONS

These results indicate that the appendix tissue contains higher number of B1 (and B) cells compared to the peripheral blood and that these cells play a role in the primary immune response to acute infection/inflammation in the appendix. Appendiceal B cell population is unique in term of CD19 intensity expression on their surface.

Three-dimensional and ultrastructural aspects of the lymphatic vascularization of the vermiform appendix

The aim of the study is to reveal the three-dimensional distribution and ultrastructure of the peripheral absorbing lymphatic vessels of the vermiform appendix, since the gut-associated lymphoid tissue is necessary to the immune responses to the enteric antigens. Corrosion casts showed the beginning of the lymphatic vascularization at the tunica mucosa, which lacks intestinal villi, through a tight, delicate lymphatic network. This network drains the lymph by peculiar straight vessels, distributed in the mucosal beams that separate the adjacent follicle domes, in the fine network of the upper portion of the lymphatic basket, surrounding the lateral walls of the basal and medium portions of each lymphoid follicle. This network, which is made of large caliber vessels that are not dilated like sinuses, continues through small vessels into the large dome-like vessels of the submucosa, which in turn by way of the lymphatic vessels of the muscular tunica, drain into the subserous precollector valved lymphatic vessels that flow into the pre-lymph node collectors. We underlined that the particular fluidity of Neoprene latex and the direct injection method, when compared with other substances and injection methods, provided us with exceptionally clear and precise three-dimensional plastic images of the absorbing lymphatic vessels. Moreover, these images extraordinarily illustrated the preservation of the absorbing lymphatic spatial relationships with blood vessels. Ultrastructural features and three-dimensional models of ultrathin serial sections of the absorbing peripheral lymphatic vessels showed a continuous endothelial wall lacking basal lamina, as well as open junctions between adjacent cells. Moreover, we observed the presence of numerous lymphocytes, together with intense transendothelial migratory activity that occurs through intraendothelial channel formations, dynamic entities, at absorbing lymphatic vessels of the peri-interfollicular lymphoid tissue. Also, we saw that the germinal center, as well as the lymphoid follicle dome, lacked lymphatic absorbing vessels. In addition, many postcapillary high endothelial venules (HEV) were observed with lymphocyte migration into the extravasal compartment. Furthermore, we maintain that the absorbing peripheral lymphatic vessels (ALPA) of the tunica mucosa play an important role in liquid drainage. For the peri-interfollicular vessels, we hypothesize a potential migratory and a reserve capacity for lymphocytes, as well as a conduction activity for the muscular tunica and submucosa vessels.

High RAD51 mRNA levels in young rabbit appendix. A role in B-cell gene conversion?

The rabbit has a limited number of VH genes that rearrange. As in the chicken, the 3'-most VH1 gene is rearranged in most B lymphocytes. This laboratory reported that by 6 weeks after birth, diversification of rearranged VH genes occurs, at least in part, by gene conversion-like events in the appendix, suggesting that this organ is a homologue of the avian bursa of Fabricius. Rad51 contributes to the repair of double-strand breaks in DNA during somatic and meiotic recombination. The gene was first identified in lower eukaryotes, and later in vertebrates including chicken, as encoding an Escherichia coli RecA-like protein. We report the cloning and sequencing of RAD51 from the rabbit. Because the chicken bursa was shown to express high levels of RAD51 message, we investigated the expression of RAD51 in the rabbit appendix and other tissues. Using a quantitative polymerase chain reaction mimic assay and conventional northern analyses, we found high RAD51 expression in young rabbit appendix comparable to levels in testis where there is an abundance of meiotic recombination. RAD51 levels were three times higher in appendix B lymphocytes compared with T lymphocytes and were lower in adult appendix, as well as in spleen and Peyer's patches of young rabbits. We measured the levels of message in several appendix cell sub-populations obtained by fluorescence-activated cell sorting and found that sub-populations of B lymphocytes corresponding to different stages of B-cell development as well as B cells undergoing isotype switch did not have significantly different mRNA levels.

B-cell superantigens may play a role in B-cell development and selection in the young rabbit appendix

In order to develop protective antibodies against a wide range of potentially infectious pathogens, the young rabbit must diversify a limited initial repertoire by somatic mechanisms (the high copy number primary repertoire). The majority of rabbit B cells produce heavy chain variable regions by rearranging the VHa allotype-encoding VH1 gene. Thus in normal rabbits the majority of serum immunoglobulins bear VHa allotype (due to VH1 FR1 and FR3 sequences). The young rabbit appendix is a site of diversification of rearranged VH genes by gene-conversion-like and somatic hypermutation mechanisms. The newly generated B cells probably undergo selection processes that involve foreign and self-antigens and superantigens. We find preferential expansion and survival of B cells in normal and VH-mutant ali/ali rabbits based on their heavy chain FR1 and FR3 sequences (VHa allotype). This selection may involve "superantigen"-like interactions with endogenous as well as exogenous ligands.

Rabbit appendix: a site of development and selection of the B cell repertoire

As early as 1963, it was proposed that the rabbit appendix was a homologue of the chicken bursa of Fabricius (ARCHER et al. 1963). The finding that the young rabbit appendix was thymus independent contributed to the concept of central primary lymphoid tissue. Today we know that appendix is a site that generates the high copy number primary repertoire through diversification of rearranged VH genes by gene conversion-like and somatic hypermutation mechanisms. Thus the appendix of young rabbits functions as a mammalian bursal equivalent. In the appendix, newly generated B cells also undergo selection processes involving self and foreign antigens and superantigens. Preferential expansion and survival of B cells in normal and mutant ali rabbits based on FR1 and FR3 expression may involve "superantigen"-like interactions with endogenous and exogenous ligands. One endogenous ligand appears to be CD5. Additional ligands may be produced by gut flora. Further studies in the rabbit model are needed to determine the fates of emigrants from primary GALT, their sites of postulated self-renewal in the periphery, and the nature of secondary diversification in secondary germinal centers where populations of B lymphocyte memory cells may develop. These data may also be helpful in understanding how the repertoire of human B cells is formed and how this repertoire might be manipulated for clinical benefit.

VH mutant rabbits lacking the VH1a2 gene develop a2+ B cells in the appendix by gene conversion-like alteration of a rearranged VH4 gene

We investigated the molecular basis for the appearance of V(H)a2 allotype-bearing B cells in mutant Alicia rabbits. The mutation arose in an a2 rabbit; mutants exhibit altered expression of V(H) genes because of a small deletion encompassing V(H)1a2, the 3'-most gene in the V(H) locus. The V(H)1 gene is the major source of V(H)a allotype because this gene is preferentially rearranged in normal rabbits. In young homozygous ali/ali animals, the levels of a2 molecules found in the serum increase with age. In adult ali/ali rabbits, 20 to 50% of serum Igs and B cells bear a2 allotypic determinants. Previous studies suggested that positive selection results in expansion of a2 allotype-bearing B cells in the appendix of young mutant ali/ali rabbits. We separated appendix cells from a 6-wk-old Alicia rabbit by FACS based on the expression of surface IgM and a2 allotype. The VDJ portion of the expressed Ig mRNA was amplified from the IgM+ a2+ and IgM+ a2- populations by reverse transcriptase-PCR. The cDNAs from both populations were cloned and sequenced. Analysis of these sequences suggested that, in a2+ B cells, the first D proximal functional gene in Alicia rabbits, V(H)4a2, rearranged and was altered further by a gene conversion-like mechanism. Upstream V(H) genes were identified as potential gene sequence donors; V(H)9 was found to be the most frequently used gene donor. Among the a2- B cells, y33 was the most frequently rearranged gene.

Human intestinal M cells exhibit enterocyte-like intermediate filaments

BACKGROUND

The derivation and ultrastructural composition of M cells covering the lymphoid follicles of Peyer's patches is still unknown. Results from different animal models have shown that there are species specific differences in the composition of intermediate filaments between M cells and neighbouring enterocytes. Little is known, however, about intermediate filaments of human M cells.

AIMS

To compare components of the cytoskeleton of human M cells with those of adjacent absorptive enterocytes.

METHODS

The expression and localisation of different cytokeratins, vimentin, and desmin in M cells was determined on follicle associated epithelia of human appendix using immunohistochemistry and immunogold electron microscopy.

RESULTS

Cytokeratins specific for human intestinal epithelial cells such as cytokeratins 8, 18, 19, and 20 were expressed in both absorptive enterocytes and M cells with no differences in intensity and cellular distribution between both cell types. Vimentin and desmin, tissue specific markers of either mesenchymal or myogenic cells, as well as other cytokeratins were not detectable in enterocytes or M cells.

CONCLUSION

This is the first study on the structure of intermediate filaments in human intestinal M cells. Our results show that in contrast to several animal models, human M cells apparently do not differ from adjacent enterocytes in the composition of their intermediate filament cytoskeleton. The presence of enterocyte like cytokeratins and the absence of other cytokeratins as well as of vimentin and desmin supports the hypothesis of an epithelial origin of human intestinal M cells and suggests that M cells may derive from differentiated enterocytes.

Eosinophils in acute appendicitis: possible significance

120 consecutive appendicectomies and 20 appendices from medicolegal autopsies were studied. The cases were grouped as. A: Acute appendicitis. B: Acute presentation, not diagnostic of acute appendicitis C: Elective appendicectomies D: Normal appendices from autopsies. Eosinophils and mast cells were counted in the muscularis, in Giemsa stained sections. The mean eosinophil and mast cell counts per mm2 were--A. 215.9; 26.5. B. 66.0; 32.1. C. 6.7; 25.8. D. 4.2; 19.6 respectively. Eosinophil count is significantly higher in A compared to others (p < 0.0001) and there was no range overlap with C and D. B is a heterogenous group with 37.5% having eosinophil counts in the range seen in A. Cases with mural eosinophil showed histological evidence of mast cell degranulation. Eosinophil infiltration of the muscularis is an early event universally seen in acute appendicitis. It is possible that the disease is triggered by Type I Hypersensitivity, and that infection is a later consequence.

In situ end labelling: effect of proteolytic enzyme pretreatment and hydrochloric acid

AIM

To determine the effect of dilute hydrochloric acid on the in situ end labelling (ISEL) reaction, with and without a variety of different proteolytic enzymes.

METHODS

Sections of tissue fixed in buffered formalin were pretreated with trypsin, protease XIV (at two different concentrations), or protease XXIV (for two different incubation times), with and without subsequent 1 M hydrochloric acid treatment. The results were compared with those obtained using hydrochloric acid alone, with proteinase K, and pepsin pretreatment, and with no pretreatment.

RESULTS

When hydrochloric acid was added to the sections in addition to trypsin, protease XIV, and protease XXIV, there was a significant increase in ISEL reactivity in both apoptotic nuclei and morphologically normal nuclei. Hydrochloric acid alone had no significant effect.

CONCLUSIONS

Hydrochloric acid has a distinctive effect on the ISEL reaction that is dependent on prior proteolytic digestion.

RAG1 and RAG2 in developing rabbit appendix subpopulations

The appendix of young rabbits is a site of primary heavy chain variable region-gene diversification and B cell selection. Appendix cells from 6- to 9-wk-old rabbits were stained and sorted for surface CD43 and IgM. We found that the CD43+IgM- and double-negative CD43-IgM- cells contained RAG1 transcripts and RAG2 protein. The presence of RAG gene products in appendix raised the possibility that pro-/pre-B cells were present in young rabbit appendix. Although an early suggestion that RAG2 plays a role in variable region-gene diversification by gene conversion in chicken bursa was not supported by studies of RAG2 protein in this tissue, we produced anti-rabbit RAG2 Abs to determine whether RAG2 protein was present in rabbit appendix, where cells that recently underwent gene conversion are found. We detected RAG2 protein in the four subpopulations of rabbit appendix lymphocytes, distinguished by surface CD43 and IgM markers. The appearance of RAG gene products during different stages of B cell maturation may reflect the function of the young rabbit appendix as a site of both B cell development and diversification.

Histochemical study of expression of lectin-reactive carbohydrate epitopes and glycoligand-binding sites in normal human appendix vermiformis, colonic mucosa, acute appendicitis and colonic adenoma

In a glycohistochemical analysis of human appendix vermiformis we report the assessment of lectin binding in cells of the Gut Associated Lymphoid Tissue of normal samples and in acute appendicitis using a panel of plant, invertebrate and mammalian lectins with specificity for alpha-L-Fuc (UEA-I), alpha-D-Gluc and alpha-D-Man (Con A), alpha-D-GalNAc (DBA), GalNAc (SBA, HPA), beta-Gal (RCA-I, 14 kDa = galectin-1) and alpha-, beta-Gal (VAA). Moreover, we initiate the study of expression of carbohydrate-binding sites in this tissue and in colonic mucosa, employing several types of carrier-immobilized carbohydrate ligands as suitable probes for this purpose. Within the three populations of macrophages intra-/subepithelial macrophages of the dome region, the lamina propria of the intercryptal region and the follicle-associated epithelium were apparently reactive with most of the lectins and also with mannose and fucose residues of the tested neoglycoproteins. Distinguishing features of germinal center macrophages in relation to intra-/subepithelial phagocytes were the lack of binding of UEA-I and DBA. In comparison to all other types of phagocytes, macrophages of the T-region displayed a rather restricted binding capacity only to Con A and RCA-I. Labeling of macrophages with SBA, HPA and VAA in this location was only rarely found. With respect to dendritic cells no consistently positive reaction was seen for follicular cells, whereas interdigitating cells of the T-region bound Con A, HPA and RCA-I, and, less frequently, SBA. Lymphocytes in all anatomical subsites of the Gut Associated Lymphoid Tissue, centrocytes, centroblasts and plasma cells had binding sites for Con A and RCA-I in common. Notably, a small number of lymphocytes mostly in the T-region but also in B-cell-rich areas expressed intranuclear binding sites for fucose and mannose residues. Intraepithelial lymphocytes and lymphatic cells of the T-region differed from lymphocytes in other regions by a more frequent expression of VAA-binding sites. The epithelium of appendix vermiformis and colonic mucosa not only presents lectin binding sites, but also has the capacity to bind carbohydrate structures, as shown by labeled glycoligand-exposing neoglycoproteins. In normal mucosa the extent of binding appeared to be associated with maturation of cells, the surface epithelium showing the most intense staining reaction. This pattern is not detectable in colonic adenoma which reveal increased intensity, when compared to normal mucosa. In contrast to development of hyperplasia, acute inflammation in appendicitis caused no detectable changes of neoglycoprotein binding. Taking our previous assessment on lectin binding in appendicitis into account, we conclude that glycosylation of goblet cell mucus, but not the capacity to bind certain sugar epitopes responds to inflammatory processes, whereas tumorigenesis of colonic adenoma can also affect the binding of neoglycoproteins.

CD5 is a potential selecting ligand for B cell surface immunoglobulin framework region sequences

In rabbits nearly all B lymphocytes express the glycoprotein CD5, in contrast to mice and humans, where only a small proportion of B cells express this molecule (Raman, C., and K.L. Knight. 1992. J. Immunol. 149:3858-3864). CD5+ B cells appear to develop early in ontogeny and be maintained throughout life by self-renewal. The function of CD5 on B cells is still unknown. We showed earlier that "positive" selection occurs during B lymphocyte development in the rabbit appendix. This selection favors B cell expressing surface immunoglobulins with VHa2 structures in the first and third framework regions (Pospisil, R., G.O. Young-Cooper, and R.G. Mage. 1995. Proc. Natl. Acad. Sci. USA. 92:6961-6965). Here we report that F(ab')2 fragments, especially those bearing VHa2 framework region determinants, specifically interact with the B cell-surface glycoprotein CD5. This interaction can be inhibited by anti-CD5 antibodies. Furthermore, immobilized F(ab')2 fragments selectively bind CD5 molecules in appendix cell lysates. Interactions of VH framework region structures with CD5 may affect maintenance and selective expansion of particular B cells and thus contribute to autostimulatory growth of autoimmune or transformed cells.

Preferential expansion and survival of B lymphocytes based on VH framework 1 and framework 3 expression: "positive" selection in appendix of normal and VH-mutant rabbits

B cells with a rearranged heavy-chain variable region VHa allotype-encoding VH1 gene segment predominate throughout the life of normal rabbits and appear to be the source of the majority of serum immunoglobulins, which thus bear VHa allotypes. The functional role(s) of these VH framework region (FR) allotypic structures has not been defined. We show here that B cells expressing surface immunoglobulin with VHa2 allotypic specificities are preferentially expanded and positively selected in the appendix of young rabbits. By flow cytometry, a higher proportion of a2+ B cells were progressing through the cell cycle (S/G2/M) compared to a2- B cells, most of which were in the G1/G0 phase of the cell cycle. The majority of appendix B cells in dark zones of germinal centers of normal 6-week-old rabbits were proliferating and very little apoptosis were observed. In contrast, in 6-week-old VH-mutant ali/ali rabbits, little cell proliferation and extensive apoptosis were observed. Nonetheless even in the absence of VH1, B cells with a2-like surface immunoglobulin had developed and expanded in the appendix of 11-week-old mutants. The numbers and tissue localization of B cells undergoing apoptosis then appeared similar to those found in 6-week-old normal appendix. Thus, B cells with immunoglobulin receptors lacking the VHa2 allotypic structures were less likely to undergo clonal expansion and maturation. These data suggest that "positive" selection of B lymphocytes through FR1 and FR3 VHa allotypic structures occurs during their development in the appendix.

Rabbit IgH sequences in appendix germinal centers: VH diversification by gene conversion-like and hypermutation mechanisms

Although the rabbit IgH locus contains approximately 100 VH genes, the majority of B cells rearrange VH1. To produce a primary repertoire containing a sufficient number of protective antibodies, rearranged VH1-DH-JH sequences may diversify within rabbit B cells in an organ that functions like a chicken bursa, sheep ileal Peyer's patch, or both. It was suggested many years ago that the rabbit appendix could be a bursal equivalent. To reexamine this possibility, we analyzed rearranged heavy chain variable region sequences in B cells from light and dark zones of appendix germinal centers from 6-week-old rabbits. Our findings indicate that antibody diversification occurs by gene conversion-like and somatic hypermutation mechanisms in appendix germinal centers of young rabbits.

Assessment of gut intraepithelial lymphocytes during late gestation and the neonatal period

Intraepithelial lymphocyte counts (IEL % enterocytes) were carried out in histological samples of jejunal, ileal and appendiceal mucosa of 39 neonates, aged from birth to 28 days. Correlations between IEL counts and developmental factors, namely gestational age, birth weight and intrauterine growth, as well as neonatal infections or feeding state were performed. No significant differences were observed among neonates grouped according to birth weight, intrauterine growth or neonatal infections. The pattern of feeding, however was associated with significantly higher IEL counts (p < 0.02) in the ileum in oral/enterally fed neonates than in the unfed or parenterally fed. Full-term neonates also had higher counts in the ileum (p < 0.02). In this group, oral/enterally fed neonates had the higher values. Thus, besides in utero development, the pattern of feeding might be considered as an important modulating factor on IEL postnatal expansion.

[The distribution of mucosal endocrinocytes in the normal human appendix and in inflammation]

The method of light microscopy was used for studying the histotopography of endocrinocytes of the vermiform process mucosa of man. The direction of their distribution was found in distal, medial and proximal parts of the vermiform process mucosa. The greatest amount of endocrinocytes in normal conditions per 1 mm2 of the mucous membrane was found in the proximal part and it was getting less towards the distal one. In inflammation there occurs an increase of the amount of endocrinocytes (in acute ordinary appendicitis, it is 1.5 times higher, in the phlegmonous form--2 times). With the development of deep destructive processes in the mucous membrane the content of endocrinocytes is sharply decreased.

Identification of M cells and their distribution in rabbit intestinal Peyer's patches and appendix

The distribution of intestinal membranous (M) cells has been studied within the follicle-associated epithelium of rabbit Peyer's patches and appendix. Vimentin expression has been assessed as a primary criterion to identify rabbit M cells in tissue sections and in whole tissue preparations. This criterion has been compared to the use of the absence of alkaline phosphatase which, due to its heterogeneous distribution within the enterocyte population, is less reliable than vimentin expression as a marker for rabbit M cells. The pattern of vimentin immunostaining revealed that the majority of M cells are located in the periphery of the follicle-associated epithelium, the dome apex being largely free of M cells. This distribution was confirmed by scanning electron microscopy. Vimentin is also expressed by follicle-associated epithelial cells in the vicinity of crypts which lack the typical lymphocyte-containing pocket of M cells. Cytoplasmic peanut agglutinin binding coincides with vimentin-expression throughout the follicle-associated epithelium but is absent from vimentin-negative enterocytes. The co-localisation of these two phenotypic markers in both M cells and epithelial cells adjacent to crypts, which lack the typical morphology of fully developed rabbit M cells, suggests that they correspond to immature M cells which by their location appear to derive directly from undifferentiated crypt stem cells and not from mature columnar enterocytes.

[Structural basis of appendiceal function in rabbits]

Enzymo-, immuno- and lactin-histochemical methods were used to study the structure of the rabbit appendix wall. The value of some structural components in the function of this part of the intestine is discussed. Some findings were documented electronmicroscopically. In addition to its resorptive function, the rabbit appendix is equipped with a potent defense mechanism against adverse environmental effects of the appendix content. Individual structures of this defensive barrier are closely characterized with regard to cellular equipment and possibilities of its morphological identification.

Age, site and distribution of subepithelial neurosecretory cells in the appendix

The appearance of subepithelial neurosecretory cells (SNC) was investigated by studying completely sampled appendices of 50 children, adolescents and adults. The cells were demonstrated using lead hematoxylin, a selective stain for neurosecretory cells. Additional routinely sampled specimens were also studied for comparison. In children up to the age of 9 yrs only occasional SNC were found. After this age, however, SNC were present in most appendices and in greater numbers. The majority of SNC were located in the distal portion of the appendix, with only small numbers of these cells being present in the proximal segment. Occasional SNC-like cells were identified in the appendiceal submucosa in all regions of the appendix at all ages. This lends support to the hypothesis that a correlation exists between the presence of increased numbers of SNC, patient age and the site distribution of both acute appendicitis and appendiceal carcinoid tumors.

Role of interleukin-6 in human and mouse mucosal IgA plasma cell responses

In summary, we have shown that human appendix and murine PP B cells, freshly isolated from normal tissue, respond IL-6 with significant increases in IgA SFC. Further, sIgA+ B cells from appendix express more IL-6R than is seen with B cells isolated from PBMC and spleen. When IgA subclass responses were measured, rhIL-6 induced both IgA1 and IgA2 SFC responses; however, 60-70% of the total response was represented by the IgA2 subclass. Our studies suggest that the human appendix as well as murine PP are enriched sources for sIgA+ B cells which are responsive to cytokines such as IL-6 for induction of IgA plasma cell responses.

Occluding junctions in the epithelia of the gut-associated lymphoid tissue (GALT) of the rabbit ileum and caecum

The zonulae occludentes of the dome epithelia and adjacent non-dome epithelia in four locations of the gut-associated lymphoid tissue (GALT) in the rabbit ileum and caecum (Peyer's patches, sacculus rotundus, caecal lymphoid patches, appendix) were studied in freeze-fracture replicas. In all locations the zonulae occludentes of the dome epithelium are composed of more junctional strands than in the corresponding non-dome epithelium. In the dome epithelia of Peyer's and caecal lymphoid patches the zonulae occludentes show considerable structural variation; the number of superimposed strands is approximately 10 (range 5-18). In the dome epithelia of sacculus rotundus and appendix, in addition to zonulae occludentes, extended networks of junctional strands (fasciae occludentes) are present particularly between M-cells and enterocytes. The zonulae occludentes consist of approximately 8 to 9 (range 5-15) superimposed strands; the fasciae occludentes extend up to a depth of 20 microns on the lateral membranes. The presence of the fasciae occludentes correlates with the appearance of regularly shaped clusters of lymphocytes, which are most developed in the dome epithelia of sacculus rotundus and appendix. These results suggest (1) that in contrast to the dome epithelia of Peyer's and caecal lymphoid patches those of sacculus rotundus and appendix are compartmentalized, and (2) that the mobility of lymphocytes and diffusion of antigens in the dome epithelia of sacculus rotundus and appendix is restricted.

The topographical and age distributions of neuroendocrine cells in the normal human appendix

In order to clarify the histogenesis of appendiceal carcinoid tumours, epithelial (ENC) and subepithelial (SNC) neuroendocrine cells were counted at four sites in 50 normal appendices stained by standard argyrophil and argentaffin techniques. In general, ENC were present in similar number at all sites within the appendix, whereas SNC were more numerous at the tip than at the base. The number of ENC was similar throughout life, apart from an increase in one neonate and some elderly patients, whereas SNC were maximal in young adults. Thus, the topographical and age distributions of SNC, but not those of ENC, parallels the topographical and age incidence of appendiceal carcinoid tumours, suggesting that most appendiceal carcinoid tumours arise from SNC rather than ENC.

Immunolocalization of integrin receptors in normal lymphoid tissues

The integrin superfamily of cell adhesion receptors consists of heterodimeric glycoproteins composed of unique alpha and beta subunits. These receptors mediate cell-substrate and cell-cell adhesive properties for a variety of cell types. This investigation has focused on the histologic distribution of the beta 1 subfamily of integrins within lymphoid tissues including tonsil, lymph node, spleen, thymus, and appendix. The dendritic cells of both follicular center and thymic origin express the alpha 1, alpha 2, alpha 3, alpha 5, and alpha 6, as well as the beta 1 integrin subunits. Most lymphoid cells in normal tissues do not express the alpha 1, alpha 2, alpha 3, alpha 5, and alpha 6 subunits, or the alpha v beta 3 integrin. The beta 1 subunit is expressed by all lymphocytes but with variable intensity. Increased levels of the alpha 5 and beta 1 subunits are observed in the follicular light zone, suggesting a role for these integrins in B-cell activation. Although the alpha 4 subunit is expressed by all lymphoid cells, an increased expression of alpha 4 and decreased expression of beta 1 by the mantle zone B-cell compartment is noted in comparison with the decreased expression of alpha 4 and increased expression of beta 1 by follicular center B-cells. These studies suggest that alpha 4 may be paired with a beta subunit other than beta 1 on the mantle zone lymphoid population. Thus, integrin expression by cells of lymphoid tissues varies with location and function and differs significantly from integrin expression observed on circulating and cultured peripheral blood lymphocytes.

Tissue localization and CD8 accessory molecule expression of T gamma delta cells in humans

In this study, we used TCR isotype-specific antibodies to examine the frequency, phenotype, and histologic localization pattern of T gamma delta cells in humans. The TCR delta 1+ cells comprised an average of 15% of the splenic CD3+ cells and 7% of circulating T cells. The T gamma delta cells in these human tissues, like their avian counterparts, were often not "double-negative" for the CD4 and CD8 accessory molecules. Approximately 50% of the splenic delta+ cells expressed CD8, and 30% of the delta+ cells in blood were CD8+. T cells of both gamma delta and alpha beta TCR isotypes were exceedingly rare in the skin. The T gamma delta cells exhibited preferential homing to the sinusoidal areas (red pulp) of the spleen and into the epithelial layer of the intestine in humans, as had been previously noted in chickens. Although 80% of the T gamma delta cells in the human intestinal mucosa were localized in the epithelial layer, these cells represented only 5 to 10% of all the CD3+ T cells in this microenvironment. We conclude that T gamma delta cells represent a sizeable subpopulation of the T cells in human peripheral tissues. The phylogenetic conservation of the CD8 expression by peripheral T gamma delta cells and of their preferential homing pattern suggests a special role in bodily defense for this T cell subpopulation.

Absence of secretory component expression by epithelial cells overlying rabbit gut-associated lymphoid tissue

The expression of secretory component by epithelial cells overlying intestinal lymphoid aggregates was examined immunocytochemically in rabbits. Intensely labeled epithelial cells were distributed along surfaces of villi surrounding follicles in jejunal and ileal Peyer's patches and along interdomal epithelium in sacculus rotundus and appendix. Secretory component labeling extended from within crypts and appendiceal crevices to the tips of villi and interdomal regions. In contrast, no immunologically detectable secretory component sites were observed in follicle-associated epithelial cells. In crypts and crevices supplying follicles, epithelial cells facing the lamina propria of villi and interdomal epithelium expressed secretory component, but cells flanking the follicle domes lacked secretory component immunostaining, with a clear demarcation between positive and negative zones at the base of the stem cell regions. These findings demonstrate a unique difference in the expression of the receptor for immunoglobulin A antibody between follicle-associated and non-follicle-associated epithelium.

Occurrence of multinucleated giant cells in the appendix of clinically healthy rabbits

The spontaneous formation of multinucleated giant cells was observed in the appendix of clinically healthy adult rabbits that were free of infection with intestinal viruses, pathogenic bacteria, fungi and parasites. Giant cells occurred singly and in aggregates. They were of the foreign body and of the Langhans' type, but intermediate forms were also noticed. Ultrastructurally, the hallmark of these appendiceal polykaryons were large phagolysomal fields harbouring amorphous debris and remains of cytoplasmic organelles and bacteria. The bacteria in the appendiceal tissues were neither of a special type nor acid-fast. The aetiology and significance of appendiceal giant cells remains to be clarified.