Acute laryngitis in the rat induced by Moraxella catarrhalis and Bordetella pertussis: number of neutrophils, dendritic cells, and T and B lymphocytes accumulating during infection in the laryngeal mucosa strongly differs in adjacent locations

Infectious laryngotracheitis results in fulminant respiratory distress. During the disease, the subglottic mucosa is selectively infected and swollen, the reason for this preference being unknown. Therefore, in the present study the immunoreaction of the laryngeal mucosa was studied in the rat after inhalation of either heat-killed Moraxella catarrhalis (PVG rats) or application of viable Bordetella pertussis (BN rats). The number of neutrophils, macrophages, dendritic cells, and T and B lymphocytes was determined in the mucosa of the supraglottic, glottic, and subglottic area of the larynx as well as in the trachea. After application of the pathogens, the mucosa of the subglottic area was significantly more affected than the glottic mucosa. Already 1 h after application of M. catarrhalis, not only neutrophils but also dendritic cells and T and B lymphocytes were found both subepithelially and within the epithelium. They showed a similar kinetic progression, although at a different level. Two hours after application of M. catarrhalis, at the peak of inflammation, dendritic cells (173 +/- 10 cells/0.1 mm2) outnumbered neutrophils (54 +/- 9 cells/0.1 mm2), T lymphocytes (25 +/- 2 cells/0.1 mm2), and B lymphocytes (4.3 cells/0.1 mm2). The subglottic area (and the trachea) contained about three to five times more cells than the glottic area. In contrast, the number of local macrophages was lower in the subglottic area (24 +/- 5 cells/0.1 mm2) compared with that of the glottic area (38 +/- 6 cells/0.1 mm2), and did not change after application of both M. catarrhalis and B. pertussis. Thus, infectious laryngotracheitis in the rat closely resembles the clinical picture in children. In addition, the present results show a major difference in cellular influx in the mucosa of the glottic and subglottic area. This demonstrates that even in two closely adjacent locations, inflammatory responses of different magnitudes can occur, and it underlines the importance of regulatory mechanisms specific for the respective microenvironment.

Lymphocyte dynamics in the pulmonary microenvironment: implications for the pathophysiology of pulmonary sarcoidosis

It is generally accepted that lymphocytes play a role in sarcoidosis. Lymphocyte numbers and in particular certain subsets are increased in the bronchoalveolar lavage fluid, and these parameters have been used as indicators for prognosis. To understand the pathophysiology of sarcoidosis the localisation and kinetics of lymphocytes in the normal lung have to be known. Lymphocytes are found in different compartments of the lung: the pulmonary vascular bed with the marginal lymphocyte pool, intraepithelial lymphocytes, the lamina propria of the bronchial tree, at a young age and under certain pathological conditions the bronchus-associated lymphoid tissue, the interstitial lymphocyte pool and the lymphocytes in the bronchoalveolar space as recovered by bronchoalveolar lavage. The lymphocyte subsets differ in these compartments. The number and subset composition are influenced by the balance of immigration, regulated by adhesion molecules, local proliferation, apoptosis and migration. In sarcoidosis lymphocyte proliferation and cell death in the bronchoalveolar space are increased several fold in the lung. More studies on regulatory factors of lymphocyte kinetics are needed in the lung of sarcoidosis patients before new therapeutic strategies can be tested.

Quantification of B, T and null lymphocyte subpopulations in the blood and lymphoid organs of the pig

Research on the pig's immune system is not only of general biological interest; the pig is also becoming more important as a large animal model in human biomedical research, e.g. as a donor for xeno-transplantation. With the increasing panel of monoclonal antibodies against porcine lymphocyte markers it is possible to gain more insight into the distribution and phenotype of lymphocyte subpopulations in the pig. In this study we investigated B cells (surface IgG: sIgG, sIgM and sIgA) and T cells (CD2, CD4, CD8, 8/1, MAC320) in the peripheral blood (pBL), thymus, spleen, tonsil, mesenteric and inguinal lymph nodes (mLN, iLN), jejunal and ileal Peyer's patches (jejPP, ilPP) in Göttingen minipigs. A flow cytometric technique was employed which enabled three color indirect immunofluorescence. B cell stained for surface IgG and surface IgA were found only in small percentages. Surface IgM positive cells were distributed at higher rates, with up to 24.9% in the iLN. Up to 64.2% of CD4+ and up to 73.1% of CD8+ cells were observed in the thymus. Most of the CD4+ cells were CD4/CD8 double positive cells. These cells were mostly triple positive in combination with CD2. A larger fraction of CD2- were CD8- which are taken to be NK cells. MAC320, a marker for a subtype of gamma/delta T cells, was predominantly found on cells in the pBL. The standardized flow cytometric technique produced comparable data on the distribution of major lymphocyte subpopulations in the blood and different lymphoid organs of the pig. The results provide a basis for future studies using the pig as animal model.

Quantification of proliferating lymphocyte subsets appearing in the intestinal lymph and the blood

Lymphocyte emigration from the intestinal wall via lymphatics is necessary to maintain gastrointestinal immunity and also to connect the different parts of the mucosal immune system. In the present study the numbers and time kinetics of proliferating lymphocyte subsets leaving the gut wall via intestinal lymphatics were analysed in mesenteric lymph node adenectomized minipigs (n = 8). After cannulation of the major intestinal lymph duct, afferent lymph was collected under non-restraining conditions. In four pigs lymphocytes taken from the intestinal lymph and blood were incubated in vitro with the thymidine analogue bromodesoxyuridine (BrdU) to label all lymphocytes in the S-phase of the cell cycle. The other four pigs received a single i.v. injection of BrdU 1 week after cannulation. The initial percentage of BrdU+ lymphocyte subsets in the intestinal lymph 15 min after BrdU injection was comparable to that after the in vitro labelling (1.5 +/- 0.7% in T cells, 10.6 +/- 1.6% in IgM+ cells and 30.0 +/- 11.9% in IgA+ cells). From this level onwards, the percentage of in vivo labelled BrdU+ lymphocyte subsets reached a maximum at 12 h after BrdU application. A different pattern of BrdU+ subsets was seen in the blood. After an early peak at around 3-4 h, the frequency of BrdU in vivo labelled cells decreased. Each subset had a maximum between 12 h and 48 h after BrdU application (maximum of BrdU+ CD2+ T cells at 12 h, 4.6 +/- 1.5%; IgM+ BrdU+ at 48 h, 8.8 +/- 3.3%). The present results provide a basis to determine the time necessary for induction of specific intestinal immunity during oral vaccination studies.

Immunohistological characterization of leukocytes in the lungs of healthy mice and after bacterial intratracheal infection

Leukocytes in the peripheral lung parenchyma of mice have not been characterized histologically during bacterial infection. The aim of this study was to investigate (a) the immunohistological characteristics of healthy murine lungs and (b) the cell kinetics during acute inflammation. BALB/c and MF1 mice were examined; as well as transgenic mice with the gene defect of cystic fibrosis (CF) in the airways as an animal model for this disease. MF1 mice served as controls for the transgenic animals. Lavaged and perfused lungs were snap frozen. B and T lymphocytes, CD4+ and CD8+ cells, dendritic cells, neutrophils and a subset of macrophages were enumerated on cryostat lung sections. The lung tissue and bronchoalveolar lavage (BAL) of BALB/c mice, infected intratracheally with Haemophilus influenzae type b (Hib), were studied at different time points after infection. In the lungs of healthy mice, including CF mice, the largest population was that of T cells, CD4+ cells being always more frequent than CD8+ cells. During acute inflammation the number of neutrophils in the lung parenchyma and BAL increased strongly within the first hours after bacterial instillation and reached baseline levels within one week. This study provides a semi-quantitative analysis of immunocompetent cells in normal and infected murine lung tissue. Differences in cell numbers are found between different strains. Moreover, the cellular reaction during Hib infection in mouse lungs is dominated by neutrophils, as expected in a primary immune response. In uninfected CF mice the numbers and distribution of immune cells in the lung tissue are normal, indicating that the cellular defense is adequate.

The influence of age and breeding conditions on the number and proliferation of intraepithelial lymphocytes in pigs

The number and subset composition of intraepithelial lymphocytes (IEL) were studied in pigs in different age groups ranging from 1 day to 4.5 years. There were no major differences between the numbers of IEL in the jejunum and ileum. The postnatal increase of IEL largely depended on the breeding conditions: in germ-free animals there was a constant level, while in conventionally bred pigs the numbers increased more obviously than in specified pathogen-free (SPF) pigs. As the numbers of IEL can rise due to increased influx from other organs, decreased emigration, decreased apoptosis or local proliferation, the incorporation of the DNA precursor bromodeoxyuridine (BrdU) by IEL was studied after different labelling protocols. There were low but definite numbers of BrdU+ IEL 1 h after BrdU, indicating in-situ proliferation in conventional animals with a tendency to a higher index in the jejunum than the ileum. Repetitive labelling protocols for 14 days resulted in 12-20% BrdU+ IEL, which may be caused by local proliferation and immigration of lymphocytes produced in other lymphoid organs as documented for the pig. Future studies need to focus on the factors regulating local proliferation and the migration of IEL in different species.

M cells at locations outside the gut

Lymphoid tissue associated with mucosal membranes is found not only along the gastrointestinal tract, but also in the tonsils, the upper and lower airways, and the conjunctiva of the eye. The epithelia overlying this mucosa-associated lymphoid tissue (MALT) contain membranous (M) cells which transport antigenic matter across the mucosal membrane to initiate immune responses. Although the morphology and function of intestinal M cells have been thoroughly studied, relatively little is known about the presence and properties of M cells in MALT outside the gut. The available data on ultrastructure, histochemistry, and antigen sampling function of the epithelia in tonsils, nasal-, larynx-, bronchus-, and conjunctiva-associated lymphoid tissue are reviewed and critically discussed. It is concluded that, in principle, the concepts of mucosal immune protection can be applied to these sites of MALT. However, it is questionable whether a separate cell type similar to intestinal M cells exists and performs antigen sampling in the different MALT epithelia. Further studies combining functional and morphological techniques are essential to understand the initiation of immune reaction at the mucosal membranes.

Activated T cells enter rat lymph nodes and Peyer's patches via high endothelial venules: survival by tissue-specific proliferation and preferential exit of CD8+ T cell progeny

Activated T cells reach the lymph nodes via afferent lymphatics but it is unknown to what extent they also enter them directly via high endothelial venules (HEV). Little is known about the mechanism mediating the proliferation of activated T cells within lymphoid tissues in vivo or the subsequent fate of the progeny. Therefore, we stimulated rat T cells via TCR and CD28 in vitro and after injection identified them in the blood and the HEV of lymphoid organs at several time points. In addition, the proliferation of these cells was studied after entering different lymphoid organs. Our results show that, firstly, activated T cells continuously enter lymph nodes and Peyer's patches directly via HEV. Second, they proliferate within lymphoid organs, the rate significantly depending on the microenvironment. Third, mainly CD8+ progeny are able to leave the tissues and re-enter the blood. Thus, the distribution of activated T cells circulating through the body can be regulated during entry, but also within the tissue by influencing their proliferation and subsequent release.

Enhanced expression of fas ligand (CD95L) on T cells after segmental allergen provocation in asthma

BACKGROUND

Little is known about the termination of the T-cell driven inflammation found in patients with allergic asthma.

OBJECTIVE

Because signals delivered through Fas/Fas ligand can lead to T-cell apoptosis, we investigated the expression of Fas and Fas ligand on peripheral blood- and bronchoalveolar lavage fluid (BALF)-derived T cells and the percentage of apoptotic BALF cells in asthma.

METHODS

Nine atopic subjects with mild asthma and 9 control subjects underwent segmental sham and allergen challenge. Flow cytometry was used to determine the T-cell expression of Fas and Fas ligand, and the terminal dUTP nick end labeled technique was applied to detect apoptotic BALF cells.

RESULTS

In asthmatic and control subjects almost all T cells in the BALF expressed Fas antigen without changes after saline or allergen challenge. A small percentage of T cells in BALF expressed the Fas ligand. In asthmatic subjects, but not in control subjects, there was a significant increase in Fas ligand after allergen challenge (CD3: 0.8% +/- 0.6% [baseline] vs 3.2% +/- 1.2% [allergen challenge]; CD4: 1.8% +/- 0.0% vs 4.3% +/- 1.8%; CD8: 2.8% +/- 2.4% vs 9.1% +/- 4.8%) but not after saline challenge, with a significant correlation to the percentage of BALF eosinophils. Apoptotic BALF cells were localized exclusively in macrophages at a very low frequency (0.03% to 0.15%) and without changes after saline or allergen challenge in both groups.

CONCLUSION

In asthma there is an upregulation of Fas ligand on T cells in BALF after allergen challenge. Because there is no evidence for increased apoptosis, this phenomenon may reflect antigen-induced T-cell activation rather than apoptosis.

Airway exposure to bacterial superantigen (SEB) induces lymphocyte-dependent airway inflammation associated with increased airway responsiveness--a model for non-allergic asthma

Although immunological consequences of systemic superantigen administration have been extensively studied, the effects of local mucosal exposure to superantigens are not well defined. The purpose of this study was to delineate the type of immune response triggered by superantigen exposure to the airway mucosa in mice. In dose-response experiments we determined a low dose of staphylococcal enterotoxin B (SEB) that triggered an inflammatory response characterized by mucosal and airway recruitment of lymphocytes, eosinophils and neutrophils together with elevated levels of IL-4, but not IFN-gamma, in bronchoalveolar lavage (BAL) fluids. TCR Vbeta analysis revealed that superantigen-responsive and -non-responsive T cells were equally recruited into the airways. SEB markedly enhanced the frequency of TNF-alpha-positive BAL macrophages as well as the amount of TNF-alpha in BAL fluids. These responses were associated with the development of increased airway responsiveness (AR) in SEB-treated mice. This effect occurred in an antibody-independent fashion. Furthermore, this type of response was observed in IgE-high responder BALB/c as well as in IgE-low/intermediate responder C57BL/6 mice. The development of increased AR was CD4+ T cell dependent as shown by transfer experiments into BALB/c nu/nu mice. These results suggest that the local immune response following mucosal superantigen administration triggers a unique inflammatory response in the airways resembling many features of "intrinsic asthma".

B and also T lymphocytes migrate via gut lymph to all lymphoid organs and the gut wall, but only IgA+ cells accumulate in the lamina propria of the intestinal mucosa

In pigs the lymphocytes emigrating from the intestinal wall were collected by cannulating the lymphatics, labeled in vitro using a fluorescent dye and retransfused. The injection of 6.6+/-4.2 x 10(8) cells resulted in a labeling index between 1.5% in intestinal lymph, 0.2% in the spleen and lymph nodes, approximately 0.1% in the intestinal lamina propria and 0.003% in intraepithelial lymphocytes. About 25 % of the injected cells were present in the blood and 1 % was recovered in the lymph. T cells were found in similar proportions in the injected and the recovered cells in the organs (70-80%). The proportion of IgA+ cells among the immigrated cells in the intestinal lamina propria ranged from 5 to 8%, which in absolute numbers was up to 60% of the injected IgA+ cells. T and IgM+ cells did not show a higher accumulation in any organ. These experiments in conventional, unrestrained animals revealed that (1) T cells immigrate into the intestinal lamina propria, (2) preferential migration of IgA+ cells from gut lymph to the intestinal lamina propria is obvious under in vivo conditions and (3) the immigrated IgA+ cells represent a very small population which is difficult to detect when analyzed in relative numbers.

Increased expression of activation markers and adhesion molecules on lung T-cells compared with blood in the normal rat

Lymphocytes play an important role in many lung diseases and are routinely accessible by bronchoalveolar lavage (BAL). Lymphocytes from the BAL (BAL pool) have a different subset composition to those from peripheral blood, consisting mainly of activated T-cells. The aim of this study was to examine whether preferential migration of activated T-cells to the bronchoalveolar space or factors of the specific microenvironment mediate this phenomenon. The expression of adhesion molecules and cellular activation markers (intercellular adhesion molecule-1, leukocyte function-associated antigen-1, CD2, CD44, interleukin-2 receptor and L-selectin) was studied on T- and B-cells not only in the BAL and peripheral blood (blood pool), but also in the compartments in between, such as the lung vascular perfusate (marginal pool) and the lung interstitium (interstitial pool), with the experiments being performed simultaneously in the same animals. Low levels of adhesion molecule expression were observed on T-cells in the blood and marginal pool, medium levels in the lung interstitium and the highest levels in the BAL. "Memory" (CD45R(low)) and "naive" (CD45R(high)) T-cells in the lung compartments showed a higher expression of adhesion molecules compared with blood. However, the predominating CD45R(low) T-cells showed a significantly higher expression than the CD45R(high) cells, indicating that CD4+ CD45R(high) T-cells had changed their phenotype to CD45R(low). In conclusion, a high level of expression of leukocyte function associated antigen-1 and intracellular adhesion molecule-1 on the bronchoalveolar lavage and interstitial T-cells is more likely to be the result of local, lung-specific induction than a prerequisite for migration into the bronchoalveolar space.

Centrally applied NPY mimics immunoactivation induced by non-analgesic doses of met-enkephalin

Neuropeptide Y (NPY) and endogenous opioids (EOPs) such as methionine-enkephalin (Met-enk) regulate similar physiological responses, but it is not known whether nociceptive and immune responses also show analogy after intracerebroventricular (i.c.v.) application. Dose-response studies show that Met-enk stimulates the blood granulocyte and splenic natural killer (NK) cell function of Lewis rats at a low dose (10(2) ng/kg, i.c.v.), whereas a high dose (10(5) ng/kg) causes suppression of innate immune functions associated with analgesia in the hot-plate test. At 15 min, 1 h and 24 h after i.c.v. application, both Met-enk (10(2) ng/kg) and NPY (1 ng/kg) produced similar effects: An initial suppression of innate immune function was followed by a long lasting stimulatory action on cell functions and serum interleukin-6 (sIL-6) levels. Thus, central NPY application resembles Met-enk-induced immunostimulation at doses not affecting nociception, suggesting an involvement of both peptides in shaping stress-induced immunomodulation of the non-analgetic form, possibly via activation of a common immunomodulatory effector mechanism.

Brain NPY Y1 receptors rapidly mediate the behavioral response to novelty and a compartment-specific modulation of granulocyte function in blood and spleen

Neuropeptide Y (NPY) alters behavioral activity and innate immune functions of rats within minutes of intracerebroventricular (i.c.v.) application. Using combinations of the Y1-5a,b(6) agonist NPY, the Y1,3,5 agonist [Leu31-Pro34]NPY (LP-NPY), and the selective Y1 antagonist BIBP3226 (BIBP), we investigated whether the NPY-Y1 receptor (Y1R) subtype regulates NPY-induced behavioral and immunological effects at 15 min after i.c.v. application. Administration of both NPY and LP-NPY decreased rearing activity in the open field and suppressed granulocyte function in the blood. These effects were blocked by BIBP pre-treatment. In contrast to the blood, NPY and BIBP+NPY treatments stimulated granulocyte function within the splenic compartment. In addition, a blood leukophilia composed of granulocytes and NK cells was induced by NPY only. We conclude that the tested early effects of NPY are mediated by either the Y1R (rearing, blood granulocyte function), or a non-Y1R (splenic granulocyte function), or by a combined receptor activation (leukocyte mobilization). Furthermore, the immunological effects of NPY demonstrate compartment specificity.

Modulation of innate immune functions by intracerebroventricularly applied neuropeptide Y: dose and time dependent effects

Centrally applied neuropeptide Y (NPY) interacts with the autonomic nervous system and the hypothalamo-pituitary-adrenal (HPA) axis activity. Since these physiological systems have been shown to modulate innate immune functions, the effects of intracerebroventricular (i.c.v.) NPY administration on leukocyte subsets in the blood, spleen and intravascular pool of the lung, blood granulocyte chemiluminescence response, and splenic natural killer (NK) cell-mediated lysis were studied in Lewis rats. Concentration-dependent NPY effects were tested at 15 min and 24 h post i.c.v. injection at dosages of 10(-6) M, 10(-9) M, and 10(-12) M. Time dependent effects were investigated at 15 min, 1 h and 24 h after i.c.v. administration of 10(-9) M NPY. Compared to saline controls, an increased number of granulocytes and NK cells in the blood, associated with a decreased granulocyte function and NK cytotoxicity was observed 15 min following NPY infusion. This initial immunosuppression was followed by long lasting stimulatory effects of NPY on the functional capacity of both cell populations when tested at 1 h and 24 h. The dosage of i.c.v. 10(-6) M NPY produced no changes, whilst 10(-9) M produced maximal, and 10(-12) M still significant effects. Results provide evidence that centrally applied NPY influences innate immunity in a dose and time dependent fashion. Cell mobilization from the vascular marginal pool is likely to be an underlying mechanism for the initial immunosuppression.

[How do medical students judge preclinical studies? Results of questionnaire analysis after the 1st and 2d year of studies]

BACKGROUND AND OBJECTIVE

For some years the evaluation of medical teaching has been demanded. In addition to questioning individual teachers, comparisons have to be made, but only a high response rate will provide representative results. A questionnaire study of medical students at the Hannover School of Medicine was undertaken to assess attendance at lectures, reasons for absence, importance of courses and practicals for passing preclinical examinations and as preparation for clinical studies.

METHODS

Questionnaires were given to two groups of students in the summer term of 1996, a) after the first year and b) after concluding the preclinical course.

RESULTS

The response rate for the two years was 92 and 87%, respectively. The reasons given for a high absentee rate at some lectures were, first of all, lack of time especially in the natural sciences--physics, chemistry and biology--but also in medical psychology, medical sociology and terminology, and secondly their lack of relevance to the clinical course. However, especially high acceptance and clinical relevance was assigned to gross anatomy. A high percentage of students were also in employment at the same time, mostly in medicine-related jobs (87%). Most students wanted continuous assessment in their compulsory subjects.

CONCLUSIONS

Regular and representative questioning of students should provide encouragement for improving the medical course and a basis for ideas on reform.

Lymphocyte subsets in distinct lung compartments show a different ability to produce interferon-gamma (IFN-gamma) during a pulmonary immune response

Lymphocytes play an important immunoregulatory role in pulmonary immune responses. By releasing cytokines they can control the cell-cell communication of other participating cells. Although it is well established that the lung lymphocytes, localized in distinct compartments, differ in their subset composition, little is known about cytokine production in these compartments during immune responses. Lewis rats were immunized by intravenous administration of sheep erythrocytes on day 0 and day 7 and challenged intratracheally with sheep erythrocytes on day 10. Four days after intratracheal (i.t.) challenge the composition of lymphocyte subsets (CD2+, CD4+, CD8+, B cells, natural killer (NK) cells) in the spleen, blood, lung perfusate, lung tissue and bronchoalveolar lavage fluid (BALF) was characterized, and intracellular IFN-gamma was detected in these subsets by flow cytometry. Comparing control and immunized animals, no changes were found in lymphocyte numbers, subsets or the percentage of IFN-gamma-producing lymphocytes in the spleen, blood and lung perfusate. In lung tissue and BALF, however, the absolute number of all lymphocyte subsets and the percentage of IFN-gamma-producing lymphocytes were increased. When the lymphocyte subsets were analysed an increased percentage of IFN-gamma-producing T cells was found in lung tissue (4.5 +/- 0.6% versus 12.8 +/- 1.1%) and in BALF (7.8 +/- 1.4% versus 14.8 +/- 1.9%) of immunized animals opposed to controls, this increase being seen in both CD4+ and CD8+ cells. Thus, there is an accumulation of T cells with an increased potential to produce IFN-gamma in the lung interstitium and the bronchoalveolar space during pulmonary immune responses.

Regeneration of implanted splenic tissue in the rat: re-innervation is host age-dependent and necessary for tissue development

The loss of spleen may lead to fatal bacterial infections. To prevent this, splenic autotransplantation has been performed in humans and experimental animals. However, there is still controversy about the protective function of this procedure. Since innervation plays an important role in splenic function, we investigated whether splenic regenerates are re-innervated, and whether this depends on the donor and host age. Splenic tissue (30 mg) was implanted into the greater omentum of either young (2 days) or old (12 months) rats, from either young or old syngeneic animals. After 3 months of regeneration, the weight of the regenerates was determined, PGP+ nerve fibers were revealed by immunohistology, and subdivided into nerve fibers of sympathetic (TH+, NPY+) or sensory (SP+, CGRP+) origin. In addition, proliferating (Ki-67 proliferation antigen+) and apoptotic cells (TUNEL technique+) were likewise investigated. No innervation of splenic regenerates was observed after implantation into old hosts, correlating with poorly developed splenic compartments. In contrast, almost normal re-innervation occurred in young hosts after implantation of both young and old splenic tissue. These regenerates showed well-developed splenic compartments and a normal number and tissue distribution of proliferating and apoptotic cells. However, after the implantation of young tissue, the final size of splenic regenerates was three times larger (140 +/- 30 vs. 40 +/- 10 mg). Thus, re-innervation of splenic implants is necessary for their subsequent development. It is determined by host age, whereas the final size of the splenic regenerates is regulated by donor age-dependent factors. This model is useful for studying both the process leading to initial innervation and the consequences of this innervation.

[The path to "Doctor of Medicine"--how do doctoral candidates evaluate their dissertation?]

BACKGROUND AND OBJECTIVE

The value of medical dissertations has for some time been controversial. Critical opinions have, on the one hand, been directed against the effort required, its duration and the concept behind these dissertations, while asserting, on the other hand, that such dissertations hinder studying and lead to unnecessary lengthening of the medical curriculum.

PARTICIPANTS AND METHOD

In collaboration with the Medical School in Hanover a questionnaire was sent to all the 189 dissertationists of one year, to be returned anonymously. It contained 16 questions about the dissertation itself, supervision. time spent on it, total duration of medical course and effect of the dissertation on the individual's medical studies. The answers were evaluated statistically by explorative data analysis.

RESULTS

181 questionnaires could be evaluated (96%). Average age of those questioned was 30.5 years, median duration of medical studies to-data was 13 semesters. For 80% it was the first attempted dissertation. 22% had been working on an entirely experimental topic (laboratory or animal experiments). The median time from starting to submitting the dissertation was 4 years, the median time of the experimental phase one year. Two-thirds of students said that work on the dissertation had not prolonged their studies. Supervision during various phases of the dissertation was overwhelmingly judged to have been "very good" or "good". Altogether 90% of dissertationists thought that it had been personally meaningful, and they would recommend it to younger costudents.

CONCLUSIONS

The results of this study show that a universal criticism of medical dissertations does not stand up to detailed enquiry. Successful dissertationists highly rated their value both to themselves and to scientific medicine. The medical dissertation should therefore firmly remain as part of medical studies and of research within them.

Bronchus-associated lymphoid tissue (BALT) and larynx-associated lymphoid tissue (LALT) are found at different frequencies in children, adolescents and adults

The lung in 98 and the larynx in 51 consecutive autopsies (age: 17th gestational week to 99 years) were studied for the presence of organized lymphoid tissue in the epiglottis and in the wall of larger bronchi. Bronchus-associated lymphoid tissue (BALT) was seen in about 40% of patients younger than 20 years of age but in older patients only in exceptional cases. In the wall of the epiglottis, however, larynx-associated lymphoid tissue (LALT) was found at a frequency of approximately 80% in patients younger than 20 years and in 56% of the patients older than 20 years. The clinical relevance of LALT as a physiological entry site for antigens or for vaccination protocols using aerosols needs to be studied in further experiments.

Comparison of the immunohistology of mucosa-associated lymphoid tissue in the larynx and lungs in cases of sudden infant death and controls

The respiratory tract of children in the first two years of life, unlike that of adults, contains bronchus-associated lymphoid tissue (BALT) and larynx-associated lymphoid tissue (LALT) with no differences in frequency between SID and control children. Using immunohistochemical methods we examined the distribution of B, T, CD4+ and CD8+ lymphocytes, HLA-D+ cells, CD68+ macrophages and proliferating cells, comparing bronchus-associated and larynx-associated lymphoid tissue of sudden infant death cases and controls. In all groups the lymphoid tissue was organized in lymphoid follicles and parafollicular areas. With no differences in the cellular composition of BALT and LALT the lymphoid follicles contained mainly B lymphocytes with some CD4+ lymphocytes in the germinal centers. Remarkably T lymphocytes of both subset types and B lymphocytes were observed in equal numbers in the parafollicular areas in contrast to gut-associated lymphoid tissue. However, the respiratory tract of young children with no differences between SID and controls might play a similar role in mucosal immunity and might function as an inductive site.

Retrospective evaluation of undergraduate medical education by doctors at the end of their residency time in hospitals: consequences for the anatomical curriculum

Reform of the undergraduate medical curriculum, including the debate on which of its parts or subjects are superfluous, is a topic of interest in many countries. On being examined at the end of their specialization period, doctors were asked to grade the relevance of all subjects in the undergraduate curriculum for training to become a medical doctor. The subjects that gained the highest grades were internal medicine, gross anatomy, physical examination course, physiology, and pharmacology. The five subjects graded least relevant were biomathematics, terminology, social medicine, medical physics, and medical chemistry. More than 80% of the doctors expressed interest in special lectures and courses, e.g., in topographic anatomy at the beginning of their postgraduate training. Retrospective evaluations at the end of residency time are helpful "evidence" to be considered in reforming the medical curriculum, and in particular in defining "core" and "optional" parts of the curriculum. The data show that anatomy is graded as highly relevant in the undergraduate medical curriculum by doctors at the end of their postgraduate training.

Lymphocyte dynamics: caution in interpreting BAL numbers

In various allergic and inflammatory lung diseases the number and subset composition of lymphocytes in the bronchoalveolar lavage (BAL) fluid are taken as indicators of the state of the disease. The number of lymphocytes in the BAL fluid depends on three main parameters: (1) entry into the bronchoalveolar space from the different compartments of the lung, (2) persistence in the bronchoalveolar space which is modified by the rate of local proliferation and apoptosis, and (3) exit into the draining bronchial lymph node via the lymphatic system. In healthy individuals lymphocytes in the BAL fluid seem to be a stable pool: each day there is hardly any entry, local cell division or cell death and few lymphocytes emigrate from this compartment. In contrast, during inflammatory, toxic and allergic reactions all parameters can increase rapidly with more lymphocytes entering, proliferating and/or undergoing apoptosis locally. Very little is known about factors such as cytokines and chemokines which may regulate these parameters. When interpreting data on lymphocyte numbers in patients, lymphocyte dynamics in the bronchoalveolar space have to be considered, and in the future it may be possible to manipulate these lymphocyte fluxes for therapeutic purposes.

The lung as a source and a target organ for T- and B-lymphocytes

In lung transplantation, a substantial number of donor leukocytes are transferred from the donor to the recipient by the graft. Using a rat model, it was analyzed in this study to what extent leukocytes leave the lung, to which phenotype they belong, and to which organs they migrate. The model used was the orthotopic transplantation of the left lung of LEW.7B(RT7b) rats into LEW(RT7a) recipients. Lung allografts are not rejected in this strain combination, which differs only in the RT7 system, a genetic polymorphism of CD45. Using the RT7b marker (monoclonal antibody His41), the distribution of donor leukocytes passively transferred with the graft was studied by immunohistology 2 wk after transplantation. At this time, 2.9 +/- 0.1% (n = 6) of the peripheral blood leukocytes in the recipients were derived from the donor lung. The donor cell population detected in the blood consisted of T cells (59 +/- 4%), B cells (5.1 +/- 0.2%) and a surprisingly high fraction of natural killer (NK) cells (36 +/- 3%). No monocytes or granulocytes were found. In lymph nodes, spleen and thymus donor-derived T- and B-cells could be shown in typical T- and B-areas, respectively. Donor-derived leukocytes were found in the liver and the skin. In the tissue and the bronchoalveolar lavage (BAL) of the host lung, predominantly T cells were found. Furthermore, in the donor tissue and BAL more than 70% of T- and B-cells were host type, demonstrating that the donor lung had been repopulated to a great extent by host lymphocytes. This supports the relevance of BAL as a diagnostic tool in lung diseases. Thus, the lung is an immunologically important site, releasing lymphocytes which migrate to other organs and also attracting many lymphocytes from the circulation.

Contribution of serum IgA to intestinal lymph IgA, and vice versa, in minipigs

Immune cells in pig gut lymph are rather well studied, but data on gut lymph immunoglobulins and their origin are nonexistent. Such data are important to understand the interplay between pig systemic and intestinal immunity as a basis for vaccination studies. In some species, gut lymph contributes much to plasma IgA, but apparently not in humans. To estimate the contributions of pig serum IgA to intestinal lymph IgA and vice versa, concentrations of IgA, IgG, IgM, albumin, haptoglobin, C3 and alpha 2-macroglobulin were measured by radial immunodiffusion in paired porcine intestinal lymph and serum samples. All proteins, except IgA, had lymph/serum ratios (< 1.0) inversely related to their size, depending on passive diffusion from serum. The mean lymph/serum ratio of IgA was 2.2 instead of an expected 0.50 or 0.65 (dimer or monomer, respectively), indicating that of the IgA in gut lymph, 22.7 or 29.5% came from serum, vs 77.3 or 70.5% from the intestine. Percentage of polymeric IgA, measured by gelfiltration and corrected radial immunodiffusion, was 64.3% in porcine mesenteric lymph and 47.3% in serum. As the pig plasma volume and daily gut lymph flow into circulation were known, it could be calculated that roughly 31% of the total plasma IgA originated daily from local intestinal synthesis, reaching blood via mesenteric lymph.

The fate of activated T cells migrating through the body: rescue from apoptosis in the tissue of origin

After activation within a lymphoid tissue, T lymphocytes enter the blood, where they circulate and then re-enter many organs. However, they predominantly end up in the tissue of origin, a phenomenon so far thought to be caused by organ-specific homing. We analyzed the fate of T cells from different sources stimulated via the T cell receptor and CD28 and then injected intravenously into rats. Our results showed that preferential proliferation and reduced apoptosis, rather than preferential immigration, were responsible for the accumulation of activated T cells in the tissue of origin, explaining how immune responses can spread from site to site but still be restricted to certain regions. Manipulating the life span of such cells might be a promising approach to influencing immune responses.

Larynx-associated lymphoid tissue (LALT) in young children

BACKGROUND

Mucosa-associated lymphoid tissue (MALT) plays a central role in mucosal immunity. Whereas the characteristics and function of MALT in the intestine are well established, almost nothing is known about MALT in the larynx.

METHODS

In this study we examined the morphology and the lymphocyte subset composition of MALT in the larynges of children who had died of sudden infant death or various defined traumatic or nontraumatic causes.

RESULTS

Organized lymphoid tissue was found in the supraglottic parts of the larynx in nearly 80% of the children in both groups. This lymphoid tissue showed all morphological signs of MALT, such as typical lymphoid follicles with germinal centers, infiltration of the overlying epithelium by lymphocytes, and high endothelial venules (HEV). Thus we will use the term LALT (larynx-associated lymphoid tissue) to refer to this tissue. The lymphoid follicles of LALT contained mainly B lymphocytes with some CD4+ lymphocytes in the germinal centers. Remarkably, T lymphocytes of both subset types and B lymphocytes were observed in comparable numbers in the parafollicular area.

CONCLUSIONS

We assume that LALT is a physiological structure of the larynx in young children. The morphology and the distribution of lymphocyte subsets are similar to those of MALT in the human gut. LALT may be a regular part of the mucosal immune system in young children with the role of respiratory inductive site for mucosal immunity.

Long-term oral application of 5-bromo-2-deoxyuridine does not reliably label proliferating immune cells in the LEW rat

To study the lifespan of immune cell populations in the LEW rat, 5-bromo-2-deoxyuridine (BrdU) was administered in the drinking water. After 12 weeks, the epithelium of gut and skin was completely BrdU+. In contrast, thymus, bone marrow, and germinal centers of Peyer's patches contained only a few BrdU+ cells, although most should have been labeled during this time. The lack of labeling was due neither to obvious toxic effects of BrdU on these organs nor to insufficient detection of incorporated BrdU. Analysis of the kinetic pattern of the appearance of BrdU+ cells in bone marrow, blood, spleen, and lymph nodes over 12 weeks revealed that the dosage of BrdU initially was high enough to label the proliferating cells in the bone marrow, but then became too low, although the BrdU uptake of the rats was similar over the entire time. This indicates that in the LEW rat the metabolism of orally applied BrdU changes over time, leading to a reduction in the amount of BrdU available for incorporation into the DNA below a level necessary for labeling all proliferating cells. This effect appears to be species- and strain-dependent, and should be considered when the BrdU technique is used.

Lymphocyte migration: an essential step in understanding the effects of vaccination

When an antigen has passed the epithelial barrier of the skin or mucosal surfaces it has to be processed and presented by accessory cells to lymphocytes. These reactions take place in lymphoid organs, such as the regional lymph nodes, Peyer's patches and tonsils, but also in the spleen if the antigen entered the blood directly. The respective lymphocyte clone expands by proliferating, and primed lymphocytes of the B and T cell series emigrate from the lymphoid organs. The traffic of lymphocytes is regulated by the interaction of a series of adhesion molecules with endothelial cells and lymphocytes. Several earlier ideas, for instance one specific "homing receptor" for each organ and different receptors for B and T lymphocytes, or exclusive migratory routes for "memory" and "naive" lymphocytes, have had to be replaced by the concept of a much more complex, multistep, cascade-type reaction. Most migration routes show "preference" rather than "selectivity". The regulation of the entry of activated T and B lymphocytes into the parenchyma of non-lymphoid organs, e.g. the lamina propria of the gut, is not as well as understood as the entry into a lymph node. A further important aspect in lymphocyte traffic is the regulation of lymphocyte migration within the organs, including the interaction between lymphoid cells and the extracellular matrix. the basic mechanisms of lymphocyte migration have to be considered when the effects of vaccination procedures are interpreted.

Autotransplantation of the spleen in the rat: donor leukocytes of the splenic fragment survive implantation to migrate and proliferate in the host

Loss of the spleen may lead to fatal bacterial infections. As a preventive procedure splenic autotransplantation has been performed in humans and experimental animals. However, there is still controversy about the protective function of this procedure, partly because the process of regeneration after implantation of splenic tissue is not fully understood. In the present study the question was addressed of whether, in contrast to the current view, leukocytes survive the phase of necrosis after implantation of splenic fragments. Rats (LEW.7A; host) received splenic fragments of a congenic rat strain (LEW.7B; donor). These fragments first underwent almost complete necrosis, then regenerated, finally developing the typical splenic compartments. Twenty weeks after implantation, leukocytes which had survived the implantation procedure (7B positive; donor) and those which had migrated from the host into the splenic implant (7B negative; host) were differentiated using a specific monoclonal antibody (anti-7B) and immunohistology. In addition, the rats received 5-bromo-2-deoxyuridine (BrdU) 1 day before the splenic autotransplant and several lymphoid and non-lymphoid organs were removed. This thymidine analogue is incorporated in proliferating cells during the S-phase of the cell cycle and can be revealed by immunohistology. The present study demonstrates that macrophages and B and T lymphocytes survive the implantation procedure and are found in the organ compartments of the splenic autotransplant. The lymphocytes proliferate and migrate into lymphoid and non-lymphoid organs. Both the number of surviving leukocytes in the splenic autotransplants and the number of donor lymphocytes found in various host organs varied considerably between single animals. Thus, not only fibroblasts but also macrophages and lymphocytes survive the avascular implantation of splenic fragments. The surviving leukocyte subsets may be involved in the regulation of the regeneration of the different splenic compartments, so increasing their numbers may finally lead to an improvement in the function of splenic autotransplants in the clinical situation.

Jejunal and ileal Peyer's patches in pigs differ in their postnatal development

The postnatal development of the jejunal and ileal Peyer's patches was studied before and after weaning in 1-, 1.5- and 2-month-old pigs. The follicles of the jejunal Peyer's patches grew with age and were two times longer and wider in specified pathogen-free and conventional pigs than in germ-free animals, thus indicating an influence of the living microbial antigens from the gut lumen. In germ-free pigs the size of the ileal Peyer's patch follicles increased between the 1st and 2nd month, whereas in the specified pathogen-free and conventional animals these follicles were comparable in size in all three age groups. In 1- to 1.5-month-old pigs the interfollicular area of jejunal Peyer's patches was wider (0.1 +/- 0.04 mm) than that of the ileal Peyer's patch (0.04 +/- 0.03 mm). Immunohistological studies showed that in germ-free pigs preferentially surface IgM+ but few IgA+ B cells were present in the follicles, domes and dome epithelia. In specified pathogen-free and conventional pigs the B cells expressed different levels of surface or cytoplasmic IgM or IgA. In all groups studied, more T cells were observed in the jejunal than in the ileal Peyer's patch. Here, few T lymphocytes were found because of the small interfollicular areas. Small numbers of Null cells were distributed in the interfollicular regions of all animals. The results show that living microbial antigens have a major influence on the jejunal and ileal Peyer's patches in pigs. The morphological differences between the two types of Peyer's patches are an indication that they develop differently during postnatal life. So far it remains unclear whether these morphological differences reflect a specific function of the pig's ileal Peyer's patch, such as the expansion of the genetically determined B cell repertoire as has been reported for sheep.

The marginal blood pool of the rat contains not only granulocytes, but also lymphocytes, NK-cells and monocytes: a second intravascular compartment, its cellular composition, adhesion molecule expression and interaction with the peripheral blood pool

To leave the blood, leucocytes marginate to the vessel wall. Granulocytes thereby form the so-called marginal pool. It is unclear to what extent such a second intravascular compartment also exists for lymphocytes subsets, NK-cells and monocytes. Samples of the peripheral blood and the marginal pool of the LEW rat were analysed by flow cytometry. In the marginal pool the percentage of granulocytes and monocytes was significantly higher compared to that of the peripheral blood, and the proportion of 'naive' T and B lymphocytes was decreased. The expression of LFA-1 was higher on all leucocyte subsets of the marginal pool except the granulocytes, whereas no differences were seen for the expression of other adhesion molecules (alpha 4-integrins, ICAM-1, CD2, L-selectin, and CD44). In addition, splenectomy influenced the cellular composition of peripheral blood and marginal pool differently and, after injection of blood leucocytes, these cells were found in both compartments showing its characteristic cellular composition. Thus, not only granulocytes, but also B and T lymphocyte subsets, NK-cells and monocytes form a second distinct intravascular compartment. This marginal pool probably influences the cellular composition of leucocyte subsets available for entry into the tissues.

Comparison of lymphocyte subsets, monocytes, and NK cells in three different lung compartments and peripheral blood in the rat

Investigations on leukocyte populations in the lung have shown that lymphocytes are found in different anatomical compartments. Lymphocytes can be seen to a different extent in the lung interstitium, the epithelium and lamina propria of the bronchi, the bronchoalveolar space, and the marginal lung vascular bed. Previous studies focused on one compartment only, or a mixture of leukocytes from lung homogenates were prepared. This study compared cellular yields from the lung parenchyma, the bronchoalveolar space, and the perfusate of the lung vasculature of healthy male Lewis rats. All compartments were investigated in the same animal, and seven different lymphocyte subsets, monocytes, and natural killer (NK) cells were analyzed using flow cytometry. It was found that the perfusate contained a high proportion of CD4+ lymphocytes compared to the lung interstitium. A very high proportion of CD4+ lymphocytes in the bronchoalveolar lavage (BAL) expressed markers for "memory" T cells. Compared to the blood, the percentage of B and T cells was much lower in the perfusate, whereas the NK cells and monocytes were more frequent. Analysis of leukocyte subsets within all compartments revealed specific, distinguishable cell compositions. Extraction of interstitial lung cells was performed using two different methods. Enzymatic digestion of the lung tissue was compared with a mechanical disruption method. Hardly any differences were observed between the two methods regarding the distribution of lymphocyte subsets, monocytes, and NK cells. These data document the need to study more than one compartment before extrapolating to lymphocytes in the lung in general. Furthermore, changes in numbers of leukocytes and subsets can now be studied in models of lung infections and immune reactions, including the entry from the blood and intrapulmonary migration from one lung compartment to the other.

The respiratory immune system of pigs

Respiratory tract infections with bacteria like Actinobacillus pleuropneumoniae are extremely common in pigs and are of major veterinary relevance. The respiratory tract can be divided into the upper part, consisting of the nose, pharynx, larynx and trachea, and the lower part, consisting of the different parts of the lung. After bronchoscopy and bronchoalveolar lavage (BAL) had been established for pigs, interest grew in the unspecific parts of the immune system of the respiratory tract (such as macrophages, mast cells, the mucociliary function) and the specific immune system, consisting of the different lymphocyte subsets. In contrast to the rodent and human lung, the lung of the pig contains large numbers of intravascular macrophages with a high clearance capacity. The main focus of this paper is the localization, subset composition and quantification of lymphocytes in the pig lung: the intravascular and interstitial pool and the lymphocytes in the bronchial epithelium and lamina propria including bronchus-associated lymphoid tissue form the major compartments. In the BAL only a small proportion of nucleated cells are lymphocytes. The effects of age, antigen exposition, immunization and infection on the lymphocyte distribution in the pig lung are presented. In addition to veterinary aspects, the lung of pigs can also serve as a model for diseases in humans.

Both activated and nonactivated leukocytes from the periphery continuously enter the thymic medulla of adult rats: phenotypes, sources and magnitude of traffic

Although the thymus is primarily noted for the export of T cells to the periphery, a small influx of cells has also been observed. It is still a matter of debate whether entry into the thymus depends on prior activation. The phenotypes, sources and degree of immigration are largely unknown. We monitored by quantitative immunohistochemistry the entry of cells from the periphery into the rat thymus in three experimental models. We injected i.v. recirculating, small, nonactivated CD4+ T cell subsets, often referred to as naive (CD45RC+) and memory or antigen-experienced (CD45RC-) cells, purified from thoracic duct lymph of allotype-marked donors, allotype-marked leukocytes released from spleen or lung transplants, or leukocytes labeled in the periphery for 12 weeks during the S-phase of the cell cycle by oral application of 5-bromo-2-deoxyuridine (BrdUrd). Early after i.v. injection (0.5 h), significantly more antigen-experienced (CD45RC-) CD4+ T cells entered the thymus, and by 24 h four times as many cells from the CD45RC- subset as from the CD45RC+ subset had entered the thymus and localized to the medulla. None of the thymic entrants expressed the interleukin (IL)-2 receptor. Following spleen transplantation approximately 40% of donor cells entering the thymic medulla were T cells and approximately 55% were B cells. In contrast, from a lung transplant, approximately 85% of peripheral immigrants were T cells and approximately 10% were B cells. After both procedures, a small number of NK cells and monocytes/macrophages were found among the immigrants (< 5%). Rats were fed BrdUrd continuously for 12 weeks, a procedure which labeled approximately 30% of peripheral lymphocytes but not cortical thymocytes. BrdUrd-labeled cells were localized almost exclusively to the thymic medulla and represented approximately 10% of medullary cells. Of the thymic immigrants approximately 50% were T cells, approximately 30% were B cells (including approximately 15% IgD+ cells), approximately 15% were NK cells and the remainder (approximately 5%) were monocytes/macrophages. Only a quarter of BrdUrd-labeled cells expressed the IL-2 receptor. The thymus is continuously infiltrated by both activated and nonactivated leukocytes from the periphery, including T cells, B cells, NK cells and monocytes. These immigrants are supplied by lymphoid and nonlymphoid organs in a characteristic subset composition. Their entry is facilitated by prior antigen experience or activation. Thus, the participation of the thymic medulla in general leukocyte traffic suggests a mechanism by which the T cell repertoire could potentially be modulated by the peripheral tissues.

Age dependency of the composition of immunocompetent cells and the expression of adhesion molecules in rat laryngeal mucosa

Clinical evidence shows that laryngeal infections in infants differ significantly from those in adults. Therefore, the composition of the mucosal immune system (granulocytes, macrophages, dendritic cells, natural killer cells, and T and B lymphocytes) and the epithelial expression of class II-MHC molecules and adhesion molecules ICAM-1, VCAM-1, and E-selectin were studied in the larynx of newborn, 5-week-old, and 3-year-old rats. With the exception of macrophages, the immunocompetent cells began to immigrate into the laryngeal mucosa after birth, indicating that the laryngeal mucosa in newborn rats is immature. In contrast, ICAM-1 was already expressed. The number of immunocompetent cells and the expression of epithelial class II-MHC and ICAM-1 increased with age. Immunocompetent cells and epithelial class II-MHC and ICAM-1 expression were mainly detected in the subglottic region, but were almost absent in the vocal fold region.

The mucosa of the middle ear and Eustachian tube in the young rat: number of granulocytes, macrophages, dendritic cells, NK cells and T and B lymphocytes in healthy animals and during otitis media

To gain a better understanding of immune reactions during otitis media, the middle ear and Eustachian tube mucosa were studied as a unit in young rats with respect to the composition of immunocompetent cells before and after middle ear infection via the tube. Using immunohistology, the distribution of NK cells, important for the defence against viral antigens, and of dendritic cells, known to be most capable of antigen uptake, processing and presentation, was determined. Furthermore, the composition of cells of the unspecific immune system (i.e. granulocytes and macrophages) and the specific immune system (i.e. T and B lymphocytes) was studied. Macrophages and dendritic cells were spread over the whole middle ear mucosa, whereas only few NK cells and T and B lymphocytes and almost no granulocytes were detected. In the Eustachian tube mucosa, immunocompetent cells, with the exception of dendritic cells and macrophages, were only rarely seen. After induction of otitis media by severing the soft palate, immunocompetent cells increased in both the middle ear and Eustachian tube mucosa, but surprisingly they were almost absent from the area of the tubal orifice to the middle ear. The results indicate that immune reactions take place similarly in the Eustachian tube and in the middle ear mucosa.

Blood leucocyte subsets of the rat: expression of adhesion molecules and localization within high endothelial venules

Although several distinct adhesion pathways are now well characterized, it is not clear whether analysis of adhesion molecule expression on leucocytes is sufficient to predict their interaction with endothelium in vivo. Therefore, in the present study this question was addressed by investigating the interaction between blood leucocyte subsets and high endothelial venules (HEV). The expression of different types of adhesion molecule (CD44, alpha 4-integrins, LFA-1, ICAM-1, CD2 and L-selectin) on lymphocytes, NK cells, monocytes and granulocytes of rat blood was determined by flow cytometry. In the same animals the numbers of blood leucocyte subsets present in the HEV of axillary lymph nodes and Peyer's patches were analysed using immunohistology. In the HEV of both axillary lymph nodes and of Peyer's patches lymphocytes (greater than 10,000 per mm2), as well as small numbers of NK cells and monocytes (less than 500 per mm2), were found. In contrast, granulocytes were not detected here. Lymphocytes, NK cells, monocytes and granulocytes each expressed CD44, alpha 4-integrins, LFA-1, ICAM-1, CD2 and L-selectin in a pattern characteristic to cell type, but this did not correlate with the different ability of the leucocyte subsets to interact with the two types of HEV. In conclusion, determining the expression of CD44, alpha 4-integrins, LFA-1, ICAM-1, CD2 and L-selectin on blood leucocytes alone is not sufficient to predict leucocyte/endothelium interaction in vivo.

Induction of protective immunity by aerosol or oral application of candidate vaccines in a dose-controlled pig aerosol infection model

In order to outline basic concepts for the design of a bacterial aerosol infection model, the development of a pig model with Actinobacillus pleuropneumoniae is described. First, reproducibility of aerosol parameters should be maintained by optimizing generating and sampling conditions. Survival rates of the chosen strain must be predictable. Secondly, inhalation conditions for the recipients have to be standardized to enable the determination of deposition sites and the dose administered. Subsequently, dose-response relationship should be evaluated to find a suitable challenge dose. Furthermore, it seems necessary to establish methods to obtain local specimens for determination of the local immune responses. The present study demonstrates that after aerosol challenge pigs were completely protected after inhalation and partially protected after oral application of A. pleuropneumoniae vaccines and describes techniques to administer bacteria in a dose-dependent, viable way. Using the infection model several stages of the disease from acute pleuropneumonia to chronic infection can be induced for research purposes.

Distribution of immunocompetent cells in various areas in the normal laryngeal mucosa of the rat

The larynx can be divided into a supraglottic, a glottic and a subglottic area, each serving different functions. In many cases of laryngitis the site of infection is located in one area, leaving other areas unaffected. It seems reasonable to speculate that the underlying cause of the heterogeneous infection pattern in the larynx is the different processing of infectious agents. Therefore, the number and distribution of granulocytes, macrophages, dendritic cells, natural killer cells and T and B lymphocytes in the normal laryngeal mucosa of young rats were studied. The results show that, with the exception of granulocytes, all subpopulations were present in different numbers. Many macrophages and dendritic cells but only a few natural killer cells and T and B lymphocytes were located in the mucosa. Dendritic cells, natural killer cells and T and B lymphocytes were rarely present in the vocal fold area, whereas in the subglottic area they were present in high numbers. Thus, differences in the composition of immunocompetent cell populations between laryngeal areas were detectable.

Ultrastructural localization of the intercellular adhesion molecule (ICAM-1) on the cell surface of high endothelial venules in lymph nodes

BACKGROUND

The high endothelial venules (HEV) in the lymph nodes are essential for lymphocyte recirculation. As a first step, the HEV surface interacts with lymphocytes through adhesion molecules. It is important to know where adhesion molecules are expressed on the surface ultrastructure and how these structures interact with lymphocytes.

METHODS

To demonstrate the ultrastructural mechanism of interaction between the HEV surface and lymphocytes through the intercellular adhesion molecule (ICAM-1), rat mesenteric lymph nodes were perfused through the superior mesenteric artery with the primary antibody (antirat ICAM-1 antibody) and secondary antibody (antimouse IgG coupled to 15 nm gold particles), which were diluted with hypothermic University of Wisconsin (UW) solution. After the immunoreaction, we analyzed the HEV three-dimensionally and quantitatively using immunoscanning electron microscopy (ISEM) combined with transmission electron microscopy (TEM).

RESULTS

HEV expressed ICAM-1 in a 5-30-fold higher concentration than other vessels. Its distribution was extensive over the luminal surface of the cell down to the junctional area. The endothelial surface of HEV undulated to form branched microfolds, along which ICAM-1 was expressed. Cytoplasmic processes of lymphocytes were seen in microfurrows between microfolds and adhered to the sides of the folds.

CONCLUSIONS

These observations imply that the microfolds expressing ICAM-1 and microfurrows are specific ultrastructural features for trapping lymphocytes, thus initiating lymphocyte emigration into the lymph node parenchyma.

M cells in Peyer's patches of the intestine

M cells are specialized epithelial cells of the mucosa-associated lymphoid tissues. A characteristic of M cells is that they transport antigens from the lumen to cells of the immune system, thereby initiating an immune response or tolerance. Soluble macromolecules, small particles, and also entire microorganisms are transported by M cells. The interactions of these substances with the M cell surface, their transcytosis, and the role of associated lymphoid cells are reviewed in detail. The ultrastructure and several immuno- and lectin-histochemical properties of M cells vary according to species and location along the intestine. We present updated reports on these variations, on identification markers, and on the origin and differentiation of M cells. The immunological significance of M cells and their functional relationship to lymphocytes and antigenpresenting cells are critically reviewed. The current knowledge on M cells in mucosa-associated lymphoid tissues outside the gut is briefly outlined. Clinical implications for drug deliver, infection, and vaccine development are discussed.

Lymphocyte traffic through lymph nodes and Peyer's patches of the rat: B- and T-cell-specific migration patterns within the tissue, and their dependence on splenic tissue

The migration routes of lymphocyte subsets through organ compartments are of importance when trying to understand the local events taking place during immune responses. We have therefore studied the traffic of B, T, CD4(+), and CD8(+ )lymphocytes through lymph nodes and Peyer s patches. At various time points after injection into the rat, labeled lymphocytes were localized, and their phenotype characterized in cryostat sections using immunohistochemistry. Morphometry was also performed, and the recovery of 51Cr-labeled lymphocytes in these organs was determined. B and T lymphocytes entered the lymph nodes via the high endothelial venules in similar numbers. Most B lymphocytes migrated via the paracortex (T cell area) into the cortex (B cell area), and then back in substantial numbers into the paracortex. In contrast, T lymphocytes predominantly migrated into the paracortex and were rarely seen in the cortex. No obvious differences were seen between various lymph nodes and Peyer s patches and the routes of CD4(+) and CD8(+)lymphocytes. After injection of lymphocytes into animals with autotransplanted splenic tissue, the number of B lymphocytes that had migrated into the B cell area of lymph nodes and of Peyer s patches was significantly decreased, whereas CD4(+) lymphocytes migrated in larger numbers into the T cell area of both organs.