T Cell Responses and Regulation and the Impact of In Vitro IL-10 and TGF-β Modulation During Treatment of Active Tuberculosis

Mycobacterium tuberculosis (Mtb) is particularly challenging for the immune system being an intracellular pathogen, and a variety of T cell subpopulations are activated by the host defence mechanism. In this study, we investigated T cell responses and regulation in active TB patients with drug-sensitive Mtb (N = 18) during 24 weeks of efficient anti-TB therapy. T cell activation, differentiation, regulatory T cell (Treg) subsets, Mtb-induced T cell proliferation and in vitro IL-10 and TGF-β modulation were analysed by flow cytometry at baseline and after 8 and 24 weeks of therapy, while soluble cytokines in culture supernatants were analysed by a 9-plex Luminex assay. Successful treatment resulted in significantly reduced co-expression of HLA-DR/CD38 and PD-1/CD38 on both CD4⁺ and CD8⁺ T cells, while the fraction of CD4⁺ CD25^high CD127^low Tregs (P = 0.017) and CD4⁺ CD25^high CD127^low CD147⁺ Tregs (P = 0.029) showed significant transient increase at week 8. In vitro blockade of IL-10/TGF-β upon Mtb antigen stimulation significantly lowered the fraction of ESAT-6-specific CD4⁺ CD25^high CD127^low Tregs at baseline (P = 0.047), while T cell proliferation and cytokine production were unaffected. Phenotypical and Mtb-specific T cell signatures may serve as markers of effective therapy, while the IL-10/TGF-β pathway could be a target for early inhibition to facilitate Mtb clearance. However, larger clinical studies are needed for verification before concluding.

Early dynamics of T helper cell cytokines and T regulatory cells in response to treatment of active Mycobacterium tuberculosis infection

Biomarkers that can identify tuberculosis (TB) disease and serve as markers for efficient therapy are requested. We have studied T cell cytokine production [interferon (IFN)-γ, interleukin (IL)-2, tumour necrosis factor (TNF)-α] and degranulation (CD107a) as well as subsets of CD4(+) T regulatory cells (Tregs ) after in-vitro Mycobacterium tuberculosis (Mtb) antigen stimulation [early secretory antigenic target (ESAT)-6, culture filtrate protein (CFP)-10, antigen 85 (Ag85)] in 32 patients with active tuberculosis (TB) disease throughout 24 weeks of effective TB treatment. A significant decline in the fraction of Mtb-specific total IFN-γ and single IFN-γ-producing T cells was already observed after 2 weeks of treatment, whereas the pool of single IL-2(+) cells increased over time for both CD4(+) and CD8(+) T cells. The Treg subsets CD25(high) CD127(low) , CD25(high) CD147(++) and CD25(high) CD127(low) CD161(+) expanded significantly after Mtb antigen stimulation in vitro at all time-points, whereas the CD25(high) CD127(low) CD39(+) Tregs remained unchanged. The fraction of CD25(high) CD127(low) Tregs increased after 8 weeks of treatment. Thus, we revealed an opposing shift of Tregs and intracellular cytokine production during treatment. This may indicate that functional signatures of the CD4(+) and CD8(+) T cells can serve as immunological correlates of early curative host responses. Whether such signatures can be used as biomarkers in monitoring and follow-up of TB treatment needs to be explored further.

IP-10 differentiates between active and latent tuberculosis irrespective of HIV status and declines during therapy

OBJECTIVES

Biomarkers for diagnosis and therapy efficacy in tuberculosis (TB) are requested. We have studied biomarkers that may differentiate between active and latent TB infection (LTBI), the influence of HIV infection and changes during anti-TB chemotherapy.

METHODS

Thirty-eight plasma cytokines, assessed by multiplex and enzyme immunoassays, were analyzed in patients with active TB before and during 24 weeks of anti-TB chemotherapy (n = 65), from individuals with LTBI (n = 34) and from QuantiFERON-TB (QFT) negative controls (n = 65). The study participants were grouped according to HIV status.

RESULTS

Plasma levels of the CXC chemokine IP-10 and soluble TNF receptor type 2 (sTNFr2) significantly differentiated active TB from the LTBI group, irrespective of HIV status. In the HIV-infected group the sensitivity and specificity was 100% for IP-10 with a cut-off of 2547 pg/mL. Plasma IP-10 declined gradually during anti-TB chemotherapy (12-24 weeks, p = 0.002) to a level comparable to LTBI and QFT negative control groups. sTNFr2 fluctuated throughout therapy, but was decreased after 12-24 weeks (p = 0.006).

CONCLUSIONS

IP-10 distinguished with high accuracy active TB from LTBI irrespective of HIV infection and declined during anti-TB chemotherapy. Plasma IP-10 may serve as a diagnostic biomarker to differentiate between the stages of TB infection and for monitoring therapy efficacy.

Markers of microbial translocation predict hypertension in HIV-infected individuals

OBJECTIVES

The aim of the study was to test the hypothesis that microbial translocation, quantified by levels of lipopolysaccharide (LPS) and subsequent monocyte activation [soluble (sCD14)], is associated with hypertension in HIV-infected individuals.

METHODS

In this exploratory substudy, 42 patients were recruited from a larger, longitudinal HIV-infected cohort study on blood pressure. LPS and sCD14 levels were measured retrospectively at the time of nadir CD4 cell count, selecting untreated HIV-infected patients with both advanced immunodeficiency and preserved immunocompetence at the time of nadir. Patients with later sustained hypertension (n = 16) or normotension (n = 26) throughout the study were identified. LPS was analysed using the Limulus Amebocyte Lysate colorimetric assay (Lonza, Walkersville, MD) and sCD14 using an enzyme-linked immunosorbent assay (ELISA). Nonparametric statistical tests were applied.

RESULTS

In the HIV-infected patients [median (interquartile range) age 42 (32-46) years; 79% male and 81% Caucasian], LPS and sCD14 levels were both negatively correlated with nadir CD4 cell count. Plasma levels of LPS (P < 0.001) and sCD14 (P = 0.024) were elevated in patients with later hypertension compared with patients with normotension. There was a stepwise increase in the number of patients with hypertension across tertiles of LPS (P = 0.001) and sCD14 (P = 0.007). Both LPS and sCD14 were independent predictors of elevated blood pressure after adjustment for age and gender. For each 10-unit increase in LPS (range 66-272 pg/ml), the increment in mean blood pressure in the first period of blood pressure recording was 0.86 (95% confidence interval 0.31-1.41) mmHg (P = 0.003).

CONCLUSIONS

As LPS and sCD14 were both independently associated with elevated blood pressure, microbial translocation may be linked to the development of hypertension.

Combined Env- and Gag-specific T cell responses in relation to programmed death-1 receptor and CD4 T cell loss rates in human immunodeficiency virus-1 infection

Additional progression markers for human immunodeficiency virus (HIV) infection are warranted. In this study we related antigen-specific responses in CD4(+) and CD8(+) T cells to CD38, reflecting chronic immune activation, and to CD4(+) T cell loss rates. Clones transiently expressing CD107a (CD8(+)) or CD154 (CD4(+)) in response to Gag, Env and Nef overlapping peptide pools were identified, along with their expression of the inhibitory programmed death-1 receptor (PD-1) in fresh peripheral blood mononuclear cells (PBMC) from 31 patients off antiretroviral treatment (ART). HIV-specific CD8(+) T cell responses dominated over CD4(+) T cell responses, and among CD8(+) responses, Gag and Nef responses were higher than Env-responses (P < 0.01). PD-1 on CD8(+) HIV-specific subsets was higher than CMV-specific CD8(+) cells (P < 0.01), whereas PD-1 on HIV-specific CD4(+) cells was similar to PD-1 on CMV-specific CD4(+) cells. Gag and Env CD8(+) responses correlated oppositely to the CD4 loss rate. Env/Gag CD8(+) response ratios, independently of PD-1 levels, correlated more strongly to CD4 change rates (r = -0.50 to -0.77, P < 0.01) than the total number of Gag-specific CD8(+) cells (r = 0.44-0.85, P < or = 0.02). The Env/Gag ratio performed better than CD38 and HIV-RNA in logistic regression analysis predicting CD4 change rate as a measure of progression. In conclusion, HIV-specific CD8(+)CD107a(+) Env/Gag response ratio was a stronger predictor for progression than CD38 and HIV-RNA. The Env/Gag ratio may reflect the balance between possibly beneficial (Gag) and detrimental (Env) CD8(+) T cell responses and should be explored further as a progression marker.

Predictive value of immunologic parameters and HIV RNA in relation to humoral pneumococcal polysaccharide vaccine responses in patients with HIV infection

In the study presented here immunologic markers and HIV RNA were related to specific antibody responses in 50 HIV-infected patients who had moderate immunodeficiency (median CD4+, 295) and were vaccinated with a pneumococcal polysaccharide vaccine. Low responses were associated with low IgG2 or high IgM levels ( P=0.01) and good responses with high IgG4 ( P=0.05) or IgG2 ( P=0.07) or low beta(2) microglobulin ( P=0.04) levels. A combination of IgG2 levels >1.0 g/l and IgM <1.6 g/l at baseline significantly predicted a twofold or better response in logistic regression analysis ( P=0.025). Neither CD4+ lymphocyte counts nor HIV RNA levels were predictive, but it should be noted that good antibody responses were not restricted to patients with high CD4+ cell counts or low HIV RNA levels.

Immunophenotypic analyses of CD34(+) cell subsets in bone marrow from HIV-infected patients during highly- active antiretroviral therapy

BACKGROUND

Because increased bone marrow lymphopoiesis might contribute to immunologic reconstitution during highly-active antiretroviral therapy (HAART), we examined the effect of HAART on CD34(+) cell subsets in bone marrow from HIV-infected patients.

MATERIALS AND METHODS

In 12 HIV-infected patients, bone marrow and peripheral blood were collected before then 4 and 26 weeks after initiating HAART. Bone marrow in 28 HIV-seronegative controls was also examined. Immunophenotypic analyses of CD34(+) cell subsets in bone marrow were performed by flow cytometry.

RESULTS

Our main findings in bone marrow were: (i) HIV-infected patients had increased proportions of CD34(+)cells expressing T- and B-cell markers before initiating HAART; (ii) in contrast, these patients had decreased proportions of CD34(+) cells expressing myeloid-associated markers; (iii) although HAART induced an increase in peripheral T-cell counts, the percentage of CD34(+)cells expressing T-cell markers tended to decrease during such therapy; (iv) HAART induced a decrease in serum IgG accompanied by a slight decrease in the proportion of CD34(+)cells expressing B-cell markers; (v) in contrast, HAART induced a significant increase in peripheral granulocyte counts, accompanied by a slightly increased proportion of CD34(+) cells expressing myeloid-associated molecules.

CONCLUSION

Our findings are compatible with an HIV-related block in T-cell differentiation, leading to accumulation of T-cell progenitors in bone marrow, and such a block may be removed by HAART.

Cytomegalovirus DNA concentration in plasma predicts development of cytomegalovirus disease in kidney transplant recipients

The clinical significance of cytomegalovirus (CMV) DNA detection in post-kidney transplantation infection surveillance was examined by comparing the performance of three assays for detection of CMV in blood: the test for CMV-pp65-antigen in leukocytes, which is routinely employed in our laboratory, the quantitative plasma CMV-DNA-polymerase chain reaction (PCR; Cobas Amplicor CMV Monitor test) and the qualitative plasma CMV-DNA-PCR (Amplicor CMV test). Thirteen kidney transplant recipients were monitored with serial samples taken over a period of 3 months following transplantation. The quantitative CMV-PCR was the test with highest sensitivity, 95.9%, vs. 88.9% and 76.9% for the CMV-pp65 antigen assay and qualitative CMV-PCR, respectively. The virus load in the first positive specimens, assessed as DNA-copies/mL, was significantly associated with CMV disease because five of the six patients who developed disease, but only one of the seven who did not develop disease, had more than 3000 CMV-DNA-copies/mL. The number of CMV-pp65 antigen-positive cells in the first positive specimens did not have predictive value for development of CMV disease. Assessment of CMV in plasma by the quantitative CMV-PCR is especially useful since it has a high sensitivity and the amount of CMV DNA in plasma is a good predictor of CMV disease.

Human intestinal endothelium shows high susceptibility to cytomegalovirus and altered expression of adhesion molecules after infection

Human cytomegalovirus (HCMV) causes gastro intestinal disease with ulcerations, apparently as a consequence of cytopathic damage to endothelial cells (EC) and subsequent microvascular obliteration. In this study we showed that cultured human intestinal microvascular endothelial cells (HIMEC) are much more susceptible to HCMV infection than human umbilical vein endothelial cells (HUVEC). When both cell types were challenged with a clinical isolate of HCMV (10 pfu per cell), 30% of HIMEC expressed HCMV immediate early proteins, but only 10% of HUVEC. Enhanced susceptibility was also reflected in the expression of early and late HCMV proteins. In addition, the interleukin-1beta (IL-1beta)-induced cellular expression of adhesion molecules differed between HIMEC and HUVEC after HCMV-infection. E-selectin was unaffected in HUVEC but increased in HIMEC, whereas vascular cell adhesion molecule (VCAM)-1 was increased in HUVEC but decreased in HIMEC. Furthermore, HCMV-infection enhanced the expression of intercellular adhesion molecule (ICAM)-1 in both cell types. In conclusion, the enhanced susceptibility to HCMV infection observed in HIMEC and the elevated expression of E-selectin and ICAM-1 observed in these cells may provide an indication to the liability of developing gastrointestinal HCMV disease and may have a possible relevance to the survival of intestinal transplants.

IL-10 in HIV infection: increasing serum IL-10 levels with disease progression--down-regulatory effect of potent anti-retroviral therapy

To examine the potential pathogenic role of IL-10 in HIV infection, we measured serum IL-10 levels in 51 HIV-infected patients and 23 healthy controls both on cross-sectional and longitudinal testing. All clinical groups (Centers for Disease Control (CDC) categories) of HIV-infected patients had significantly higher circulating IL-10 levels than controls, with the highest levels among the AIDS patients, particularly in patients with ongoing Mycobacterium avium complex (MAC) infection. Among 32 HIV-infected patients followed with longitudinal testing (median observation time 39 months), patients with disease progression had increasing IL-10 levels in serum, in contrast to non-progressing patients where levels were stable. While both IL-10 and tumour necrosis factor-alpha (TNF-alpha) increased in patients with disease progression, the IL-10/TNF-alpha ratio decreased in these patients, suggesting imbalance between these two cytokines. Finally, we found that highly active anti-retroviral therapy (HAART) induced a significant, gradual decrease in IL-10 levels but without normalization. These findings suggest a pathogenic role for IL-10 in HIV infection, and may suggest a possible role for immunomodulating therapy which down-regulates IL-10 activity in addition to concomitant potent anti-retroviral therapy in HIV-infected patients.

CD4+ and CD8+ lymphocytes and HIV RNA in HIV infection: high baseline counts and in particular rapid decrease of CD8+ lymphocytes predict AIDS

OBJECTIVE

To study the progression of HIV infection in relation to immunological and virological variables with emphasis on the role of CD8+ lymphocytes.

DESIGN

Prospective follow-up from October 1991 of patients observed for at least 18 months allowing nucleoside analogue monotherapy. Peripheral CD4+ and CD8+ lymphocyte counts, HIV RNA, and soluble CD8 were analysed by statistics allowing the evaluation of serial data, avoiding time points with concurrent infections.

SETTING

Tertiary university clinic.

PATIENTS

Forty-nine patients were followed for 52.6 months, baseline CD4+ count of 300 x 10(6)/l, sample interval of 5.9 months (medians).

MAIN OUTCOME MEASURES

AIDS, death, and CDC groups B- or C-related events.

RESULTS

AIDS developed in 28% of patients. Baseline CD8+ counts above the median were significantly associated with AIDS development; the best Cox model included CD8+ cells and the log10RNA/CD4 ratio. A decline in CD8+ counts relative to baseline most significantly predicted AIDS, along with higher baseline RNA and actual CD4+ counts of less than 200 x 10(6)/l. Levels of soluble CD8 in the blood relative to total CD8+ cells significantly increased in patients developing AIDS. Death occurred in 16% of the patients, and was only predicted by high CD8+ cell counts at baseline. CDC B- and C-related events occurred in 35% of the patients and were best predicted by high baseline CD8+ counts and high RNA levels.

CONCLUSIONS

The serial quantitation of CD8+ lymphocytes gave highly significant predictive information on the natural progression of HIV infection in patients with moderate to severe immune deficiency. Our data suggest that the hyperactivation of CD8+ lymphocytes is an important factor leading to a numerical decrease of CD8+ lymphocytes in progressive HIV infection.

Different regulatory pathways employed in cytokine-enhanced expression of secretory component and epithelial HLA class I genes

The transmembrane secretory component (SC, or pIg receptor) plays a crucial role in mucosal immunity by translocating dimeric IgA and pentameric IgM through exocrine epithelia. This receptor is up-regulated by cytokines in parallel with increased epithelial HLA expression. By use of the human epithelial cell line HT-29m3, we show that IFN-gamma, TNF-alpha and IL-4 activate transcription of the SC gene. This activation was slow, suggesting mediation via newly synthesized protein factors. IFN-gamma and TNF-alpha, but not IL-4, also up-regulated expression of HLA class I genes. However, this gene induction was rapid and did not depend on new protein synthesis. Nuclear run-on experiments showed that the transcription rate of HLA class I genes nearly peaked after only 30 min of IFN-gamma or TNF-alpha stimulation, whereas the SC transcription rate did not peak until after 20-36 h of IFN-gamma, TNF-alpha or IL-4 stimulation. Gel electrophoresis mobility shift assays demonstrated binding of nuclear proteins from cytokine-stimulated HT-29 cells to consensus elements in the promoter of the SC gene, involving the binding site for the nuclear factor-kappaB p50 subunit after TNF-alpha stimulation, and IFN-stimulated response element after IFN-gamma stimulation (and weakly after TNF-alpha. Our observations in vitro likely parallel events in vivo by which activated mucosal T cells and macrophages enhance pIg receptor-mediated external transport of secretory IgA and IgM and up-regulate epithelial HLA expression.

Tumor necrosis factor (TNF) system levels in human immunodeficiency virus-infected patients during highly active antiretroviral therapy: persistent TNF activation is associated with virologic and immunologic treatment failure

Because persistent tumor necrosis factor (TNF)-alpha activation may play a pathogenic role in human immunodeficiency virus infection, TNF component levels were assessed over 78 weeks in plasma and peripheral blood mononuclear cells (PBMC) during highly active antiretroviral therapy (HAART) in 40 HIV-infected patients. HAART induced a significant decline in plasma levels of TNF-alpha and soluble TNF receptors and was associated with a fall in the abnormally increased unstimulated and a rise in the abnormally low Mycobacterium avium complex-purified-protein derivative-stimulated TNF-alpha released from PBMC. However, concentrations of these TNF components were not normalized. Patients with virologic and immunologic treatment failure after 52 weeks had higher levels of several TNF components than other patients early after initiation of therapy, also during periods with adequate virologic response. Although TNF components significantly decreased during HAART, these results support data indicating that full immunologic normalization is not achieved during such therapy. The persistent activation of the TNF system in a subgroup of persons may be involved in treatment failure.

Major histocompatibility complex class II-dependent antigen presentation by human intestinal endothelial cells

BACKGROUND & AIMS

In the normal gut, human intestinal microvascular endothelial cells (HIMECs) express major histocompatibility complex (MHC) class II molecules. Enhanced expression is found in chronic inflammation. We examined the cytokine regulation of MHC class II molecules and the associated invariant chain (Ii) in HIMECs and investigated whether such cells can process and present a complex protein antigen to T cells.

METHODS

Enzyme-linked immunosorbent assay, flow cytometry, immunoelectron microscopy, as well as T-cell activation assay with HIMECs and HLA-DR-restricted T-cell clones were employed.

RESULTS

In unstimulated HIMEC monolayers, HLA-DR, -DP, and -DQ and Ii were undetectable at the protein level, but interferon gamma (IFN-gamma) (100 U/mL) induced expression that peaked for DR after 2-3 days, for DP after 4-6 days, for DQ after 10-12 days, and for Ii after 2-3 days. Tumor necrosis factor alpha had no effect alone but enhanced class II expression in combination with IFN-gamma, most notably for DQ and DP. HLA-DR3-restricted and Mycobacterium tuberculosis heat shock 65-kilodalton-specific T-cell clones were activated to produce IFN-gamma in response to relevant antigen presented by IFN-gamma-treated HIMECs. This response was inhibited by blocking monoclonal antibody to HLA-DR and by chloroquine when compared to professional antigen-presenting cells, HIMECs activated T-cell clones quite efficiently.

CONCLUSIONS

These data suggest that microvascular endothelial cells can present complex protein antigens in the human gut.

[Q-fever imported into Norway]

Q fever is an important zoonosis that occurs throughout the world. In contrast to most other European countries, there has been no evidence of endemic Q fever in Norway up to now. The disease is caused by Coxiella burnetii, a rickettsia-like bacterium. Humans are infected mainly by inhalation of contaminated aerosols from cattle, sheep and goats. Clinical manifestations are protean, ranging from asymptomatic infection to life-threatening endocarditis. In this article we present the first four cases of serological proven acute Q fever imported into Norway. The patients were Norwegian tourists who had visited Bhutan, the Canary Islands, and Morocco. Two patients had fever with maculopapular exanthema, one had pneumonia, and one had biopsy-proven granulomatous hepatitis. Three were treated with tetracyclines. All four patients recovered well.

Topographic distribution of homing receptors on B and T cells in human gut-associated lymphoid tissue: relation of L-selectin and integrin alpha 4 beta 7 to naive and memory phenotypes

In mice, integrin alpha 4 beta 7 is the main receptor used by lymphocytes that home to the Peyer's patches, although L-selectin contributes to the initial interaction with high endothelial venules. Less is known about the expression and function of these adhesion molecules in humans. The distribution of L-selectin and alpha 4 beta 7 on various B- and T-cell subsets was examined in human Peyer's patches (n = 8) and appendix (n = 4), collectively called gut-associated lymphoid tissue. Multicolor immunophenotyping was performed on cryosections, and dispersed cells were examined by flow cytometry. In cryosections, CD45RA+ T cells around and within interfollicular high endothelial venules, as well as surface (s)IgD+ B lymphocytes in the follicle mantles, often expressed abundant L-selectin but only intermediate levels of alpha 4 beta 7. CD45RO+ T cells and sIgD- B cells expressed higher levels of alpha 4 beta 7 and were often located near putative efferent lymphatics; only a small fraction (< 20%) of such memory cells expressed L-selectin. By flow cytometry, considerably more T than B lymphocytes co-expressed L-selectin and alpha 4 beta 7 (40% versus 25% and 67% versus 39%, respectively). In samples with many L-selectin+ cells (> 30%), more of these lymphocytes co-expressed alpha 4 beta 7 than in samples with few L-selectin+ cells. Because L-selectin and alpha 4 beta 7 were co-expressed on lymphocytes located near high endothelial venules, and because such co-expression was relatively common when many L-selectin+ cells were present, both of these molecules might participate in homing to human gut-associated lymphoid tissue. Such homing is probably most pronounced for T lymphocytes that were found to express L-selectin and alpha 4 beta 7 more often than B lymphocytes. The selective and relatively high expression of alpha 4 beta 7 on memory cells located near efferent lymphatics indicated a different migratory capacity; after exit from gut-associated lymphoid tissue, such stimulated cells might home mainly to mucosal effector sites.

Intercellular adhesion molecule-1 (ICAM-1; CD54) expression in human hepatocytic cells depends on protein kinase C

BACKGROUND/AIMS

Intracellular regulation of intercellular adhesion molecule-1 has mainly been studied in lymphoid, endothelial, and epithelial cells. Intercellular adhesion molecule-1 plays a central role in many immune responses, and we have previously studied its regulation in hepatocytes. Here we report how manipulation of intracellular signal systems influenced its expression.

METHODS

The constitutive and cytokine-induced expression of intercellular adhesion molecule-1 mRNA and protein was studied in the human hepatocytic cell lines Hep G2 and SK-Hep-1.

RESULTS

When agonists and antagonists of protein kinase C, calmodulin, and protein kinase A were introduced in addition to prostaglandin E2 and a cyclooxygenase inhibitor, only the protein kinase C activator phorbol 12-myristate 13-acetate resulted in a rapid and dose-dependent increase in intercellular adhesion molecule-1 protein and mRNA. Phorbol 12-myristate 13-acetate stimulated sustained high levels of intercellular adhesion molecule-1 protein, whereas the corresponding mRNA response was biphasic, peaking at 3 h. Actinomycin D blocked the stimulatory mRNA phase, suggesting that de novo transcription was induced. Coincubation with phorbol 12-myristate 13-acetate and the protein synthesis inhibitor cycloheximide gave considerably higher mRNA levels than with phorbol 12-myristate 13-acetate alone. Protein kinase C may therefore even stimulate synthesis of proteins that speed up the turnover of intercellular adhesion molecule-1 mRNA. The protein kinase C inhibitor staurosporine abrogated the induction of intercellular adhesion molecule-1 by phorbol 12-myristate 13-acetate, indicating that this effect was indeed exerted by protein kinase C. More original was our observation that staurosporine also completely blocked the stimulatory effects of interferon-gamma, tumour necrosis factor-alpha, and interleukin-1. Recent reports have noted that these cytokines apparently use receptors which activate different intracellular pathways. We also noted that the glucocorticoid dexamethasone partially inhibited the stimulation of intercellular adhesion molecule-1 by these cytokines. This phenomenon could be important for the immunosuppressive effects of corticosteroids in patients with liver disease.

CONCLUSIONS

Our data suggest that a certain level of protein kinase C activity is mandatory for liver cells in cytokine-mediated upregulation of intercellular adhesion molecule-1.

Cytokine-regulated expression of E-selectin, intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1) in human microvascular endothelial cells

Endothelial cells (EC) recruit circulating leukocytes to sites of inflammation, partly by expression of endothelial-leukocyte adhesion molecules. Whereas the regulation of some adhesion molecules is well characterized in cultured HUVEC, similar data for microvascular human test systems are limited. We studied the cytokine-regulated expression of vascular cell adhesion molecules E-selectin, vascular cell adhesion molecule-1 (VCAM-1), and intercellular adhesion molecule-1 (ICAM-1) in cultured human intestinal microvascular endothelial cells (HIMEC). E-selectin and VCAM-1 were induced, and ICAM-1 was enhanced, in a dose-dependent fashion after stimulation with IL-1beta, TNF-alpha, and LPS. Each adhesion molecule displayed characteristic time-related responses comparable to those obtained with HUVEC, and each molecule supported adhesion of leukocytes. Notable disparities between the two endothelial test systems were that 1) expression of total cellular E-selectin (but not surface membrane expression) was sustained after 72 h of IL-1beta stimulation in HIMEC, contrasting a rapid biphasic response in HUVEC; 2) LPS did not maintain prolonged expression of ICAM-1 and VCAM-1 in HIMEC; and 3) VCAM-1 protein was dose-dependently up-regulated by IL-4 in HUVEC, peaking after 8 h, while IL-4 had only a negligible effect on the expression of this protein in HIMEC. In conclusion, the regulation of these adhesion molecules appears to be somewhat different in HIMEC compared with HUVEC, and the differences from available data on skin-derived microvascular endothelial cell cultures are to some extent substantial. Our findings document the importance of using relevant endothelial cell culture systems for studies of leukocyte-endothelial cell interactions.

Cytokine-regulated expression of E-selectin, intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1) in human microvascular endothelial cells

Endothelial cells (EC) recruit circulating leukocytes to sites of inflammation, partly by expression of endothelial-leukocyte adhesion molecules. Whereas the regulation of some adhesion molecules is well characterized in cultured HUVEC, similar data for microvascular human test systems are limited. We studied the cytokine-regulated expression of vascular cell adhesion molecules E-selectin, vascular cell adhesion molecule-1 (VCAM-1), and intercellular adhesion molecule-1 (ICAM-1) in cultured human intestinal microvascular endothelial cells (HIMEC). E-selectin and VCAM-1 were induced, and ICAM-1 was enhanced, in a dose-dependent fashion after stimulation with IL-1beta, TNF-alpha, and LPS. Each adhesion molecule displayed characteristic time-related responses comparable to those obtained with HUVEC, and each molecule supported adhesion of leukocytes. Notable disparities between the two endothelial test systems were that 1) expression of total cellular E-selectin (but not surface membrane expression) was sustained after 72 h of IL-1beta stimulation in HIMEC, contrasting a rapid biphasic response in HUVEC; 2) LPS did not maintain prolonged expression of ICAM-1 and VCAM-1 in HIMEC; and 3) VCAM-1 protein was dose-dependently up-regulated by IL-4 in HUVEC, peaking after 8 h, while IL-4 had only a negligible effect on the expression of this protein in HIMEC. In conclusion, the regulation of these adhesion molecules appears to be somewhat different in HIMEC compared with HUVEC, and the differences from available data on skin-derived microvascular endothelial cell cultures are to some extent substantial. Our findings document the importance of using relevant endothelial cell culture systems for studies of leukocyte-endothelial cell interactions.

Isolation and longterm culture of human intestinal microvascular endothelial cells

Microvascular endothelial cells play an important part in inflammation as well as in organ specific leucocyte traffic, and may be functionally different from large vessel endothelium in this respect. This study therefore established a method for isolation and longterm culture of human intestinal microvascular endothelial cells (HIMEC). After dissociation by collagenase/dispase/DNase of mucosal and submucosal tissue obtained from normal adult jejunum, cells were plated and cultured to subconfluence in endothelial serum free medium containing 2.5% fetal calf serum, hydrocortisone, and N6, O2-dibutyryladenosine cyclic monophosphate. Primary cultures were trypsinised and endothelial cells were isolated by paramagnetic beads armed with monoclonal antibody to CD31. Optimal growth conditions for HIMEC cultures were established, allowing up to nine passages (three months in vitro). The cells contained Weibel-Palade bodies, expressed von Willebrand factor, CD31, and VE-cadherin; and bound Ulex Europaeus lectin I. A method to establish longterm cell cultures of HIMEC will facilitate further investigation of the function of intestinal endothelial cells and their participation in physiological and pathological events in the gut.

Constitutive and cytokine induced expression of HLA molecules, secretory component, and intercellular adhesion molecule-1 is modulated by butyrate in the colonic epithelial cell line HT-29

Normal colonic epithelial cells play an important part in the mucosal immune system and use butyrate, a bacterial fermentation product, as an important energy source. Butyrate deficiency has been associated with inflammatory bowel disease, diversion colitis, and pseudomembranous colitis. Butyrate effects on important molecules for epithelial immune functions were studied in a colonic epithelial cell line (HT-29): the constitutive and cytokine regulated expression of secretory component (poly-Ig receptor), HLA class I and II molecules, and intercellular adhesion molecule-1 (ICAM-1). Butyrate facilitated the constitutive expression of secretory component and HLA class I. Butyrate furthermore tended to enhance cytokine mediated stimulation of protein expression, although tumour necrosis factor alpha (TNF) and interleukin 4 (IL 4) responses on HLA class I and secretory component, respectively, were relatively inhibited by butyrate. Cytokine mediated accumulation in the various mRNAs usually increased even more in the presence of butyrate, with the exception of TNF response on HLA class I and secretory component mRNA concentrations. In conclusion, butyrate may substantially influence constitutive and cytokine mediated expression of molecules with immune functions in a complex and differentiated manner, and butyrate deficiencies, as seen in various clinical conditions, might influence mucosal immune responses.

Butyrate differentially affects constitutive and cytokine-induced expression of HLA molecules, secretory component (SC), and ICAM-1 in a colonic epithelial cell line (HT-29, clone m3)

In conclusion, we have found that physiological concentrations of butyrate increase the constitutive levels of HLA class I and SC molecules in HT-29m3 cells. Moreover, butyrate at high concentrations induces de novo synthesis of HLA-DR but not ICAM-1 molecules. Our data further showed that butyrate generally facilitates the cytokine-induced expression of immunological molecules in these cells but, interestingly, it specifically reduces the stimulatory effects of TNF and IL-4 on HLA class I and SC, respectively. We are currently studying how butyrate affects transcriptional regulation of the genes encoding these molecules. Further knowledge about the effects of butyrate in relation to gene regulation is required. It is possible that butyrate might interfere with specific, cytokine-dependent regulatory elements in certain genes which, in turn, could have implications for immune regulation of colonic epithelial cells in vivo.

Expression and release of plasminogen activators, their inhibitors and receptor by human tumor cell lines

Plasminogen activators (PAs) and their inhibitors (PAIs) can be produced by tumor cells and surrounding inflammatory cells and fibroblasts. The present study evaluate both the expression and release of PAs (uPA and tPA) and PAIs (PAI-1 and PAI-2) from cultured cells, and also the expression of uPA receptor (uPAR). Immunocytochemistry showed that PAs, PAIs and uPAR were present to different extents on the surface of colon carcinoma cells (Caco-2, HT-29), malignant melanoma cells (LOX) and normal fibroblasts. uPA immunoreactivity was intermediate in Caco-2, HT-29 and LOX and weak in the fibroblasts. tPA immunoreactivity was intermediate in Caco-2 and LOX and weak in HT-29 and fibroblasts. PAI-1 and PAI-2 immunoreactivities were absent in HT-29, weak in Caco-2 and strong in fibroblasts. In LOX the immunoreactivity was intermediate for PAI-1 and strong for PAI-2. uPAR immunoreactivity was weak in Caco-2, HT-29 and LOX and negative in fibroblasts. ELISAs on conditioned medium detected that the colon carcinoma cells Caco-2 and HT-29 did not release any PAs or PAIs. LOX released tPA (median 9 ng/million cells at 72 hours), PAI-1 (1050 ng/million cells) and PAI-2 (245 ng/million cells), and fibroblasts released uPA (1 ng/million cells) and PAI-1 (910 ng/million cells). These results show that both tumor cells and fibroblasts express tissue destructive enzymes, PAs and PAIs, whereas only the tumor cells express the uPAR required for focalization and regulation of PA activity at the cell surface. The melanoma cells LOX and fibroblasts also released PAs and PAIs, in contrast to the colon carcinoma cells Caco-2 and HT-29.

Immune modulation of adhesion molecules ICAM-1 (CD54) and LFA-3 (CD58) in human hepatocytic cell lines

Interactions between leukocytes such as T cells and accessory or target cells are promoted by adhesion molecules, in particular intercellular adhesion molecule-1 (ICAM-1) and lymphocyte function-associated antigen-3 (LFA-3). Hepatocytes are usually negative for these surface membrane proteins which, however, may be up-regulated in inflammatory processes within the liver. Because the regulatory signals for, and tissue distribution of, these adhesion molecules vary among different tissues, expression of ICAM-1 and LFA-3 was studied in the Hep-G2 and SK-Hep-1 human hepatocytic cell lines in vitro. Low, constitutive membrane expression of the two molecules was detected in both cell lines. ICAM-1, but not LFA-3, was rapidly up-regulated by interleukin-1 (IL-1), tumor necrosis factor-alpha (TNF), and to some extent by interferon-gamma (IFN) and IL-6, whereas IL-4 had variable low effects, if any. Considerable synergism on ICAM-1 protein levels was observed after stimulation with TNF, IL-1, and IFN, whereas co-incubation with actinomycin D abolished these effects. ICAM-1 mRNA levels increased 16-20 times after cytokine incubation. Our data indicated that hepatocytes share the regulatory pathways for ICAM-1 described for several other cell types. Absence of these molecules in vivo may reflect a dominance of negative modulation signals in the normal liver, which might also explain the low levels of HLA class I molecules.

Interferon-gamma stimulation of messenger RNA for human secretory component (poly-Ig receptor) depends on continuous intermediate protein synthesis

Secretory component (SC or poly-Ig receptor) plays a key role in mucosal external body fluids. The aim of this study was to elucidate the molecular events underlying IFN-gamma-dependent up-regulation of SC. Using a human SC cDNA clone isolated by our laboratory, we found that IFN-gamma up-regulated SC mRNA levels in a time- and concentration-dependent manner. Moreover, in situ hybridization showed a striking increase of SC mRNA-positive HT-29 cells after IFN-gamma treatment. Inhibition with 5,6-dichloro-1-beta-ribofuranosyl-benzimidazole (DRB) indicated a half-life for IFN-gamma-induced SC mRNA of approximately 1 h. Cycloheximide (CHX) abolished the IFN-gamma-induced accumulation of SC mRNA in a reversible manner; the time-course suggested that de novo synthesis of protein factor(s) with a turnover time shorter than 6 h was required for accumulation of SC message. IFN-gamma-stimulated up-regulation of SC expression therefore appears to depend on molecular events similar to those taking place for the activation of several other genes in the Ig supergene family.

Molecular cloning and exon-intron mapping of the gene encoding human transmembrane secretory component (the poly-Ig receptor)

Secretory component (SC or the poly-Ig receptor) plays a crucial role in mucosal immunity by translocating polymeric IgA and IgM through secretory epithelial cells into external body fluids. Labeled restriction fragments from human SC cDNA were used to screen a human genomic leukocyte library. Three overlapping clones, spanning a total of 19 kb of the human SC gene, including 3 kb of the 5' flanking region, were characterized. The putative TATA box candidate, preceded by a CAAT-like box, was found 329 nucleotides upstream of the first exon. Altogether 11 exons covering the entire coding region were identified. The exon size ranged from 59 to 657 nucleotides and exon-intron junctions followed known consensus sequences. Three of the five extracellular Ig-related domains (D1, D4 and D5) were confined to one exon each (E3, E5 and E6), whereas D2 and D3 were encoded by the same exon (E4). The latter exon corresponds to that involved in alternate splicing of rabbit SC. The membrane-spanning segment was confined to part of one exon (E8). The cytoplasmic tail was encoded by four exons (E8-E11), whose boundaries encompassed fairly well the structural determinants proposed to be responsible for intracellular sorting of SC in the rabbit. The polymorphic restriction site reported earlier for Pvu II was localized to the third intron.

Epithelial expression of HLA, secretory component (poly-Ig receptor), and adhesion molecules in the human alimentary tract

Epithelial HLA class II is differentially expressed (DR >> DP) only after birth in salivary glands and small intestinal mucosa, in contrast to class I determinants and secretory component (SC) which appear early in gestation. However, there is a brisk postnatal increase in SC expression along with the class II induction, suggesting stimulation by cytokines from activated immune cells. T lymphocytes remain quite scanty in postnatal salivary glands, and the striking SC and class II expression might reflect a synergistic effect of IFN-gamma and TFN-alpha on immature epithelial cells. Enhanced epithelial expression of both SC and class II in salivary glands from sudden infant death victims could be the effect of immunostimulation caused by an infectious agent. Strikingly upregulated SC and epithelial class II expression (DR > DP > DQ) is seen in various inflammatory lesions such as obstructive sialadenitis, Sjögren's syndrome, chronic gastritis, and celiac disease. IFN-gamma and TNF-alpha are most likely involved as the expression patterns can be reproduced with these cytokines in vitro on colonic epithelial cell lines. However, these molecules of the Ig supergene family do not show a selective response in epithelia of inflammatory lesions because increased expression is also seen for lysozyme, lactoferrin and some other proteins. ICAM-1 can be upregulated on epithelial cells by various cytokines in vitro although the situation remains uncertain in mucosal inflammation. The expression pattern in IBD is complicated by dysplastic epithelial changes leading to reduced SC levels which may thus, in turn, jeopardize the poly-Ig transport mechanism. Epithelial class II molecules appear to have antigen-presenting properties, but the immunopathologic role of their increased expression in inflammatory disease in terms of induction of autoimmunity and/or abrogation of oral tolerance is a matter of continuing dispute.

Circulating secretory component in relation to early diagnosis and treatment of liver metastasis from colorectal carcinomas

AIMS

To evaluate serum secretory component in relation to early detection and clinical management of liver metastasis in patients with colorectal cancer.

METHODS

Secretory component and carcinoembryonic antigen (CEA) were analysed in serial serum samples from 23 patients who had liver metastases as the only apparent recurrence, and in sera from 54 matched controls. Results of surgical treatment of recurrences were classified peroperatively as radical when no residual tumour was apparent and resection margins were free of disease.

RESULTS

In total, 18 (78%) patients had increased secretory component during the whole follow up period (median 16 months); 12 (52%) had raised secretory component concentrations before clinical recurrence (median lead time 5.2 months). There was no difference before recurrence between circulating secretory component and CEA in sensitivity and lead times. Seventeen patients underwent surgery for hepatic metastasis; seven had radical hepatic resection of which only two (29%) showed increased secretory component concentrations before clinical recurrence; both had concurrent raised CEA values. By contrast, secretory component was raised in 83% of those cases considered inoperable.

CONCLUSIONS

Although serum secretory component clearly increases in most patients with liver metastases, its clinical value seems questionable because secretory component apparently indicates mainly inoperable hepatic metastases.

Expression and regulation of adhesion molecules ICAM-1 (CD54) and LFA-3 (CD58) in human intestinal epithelial cell lines

T cells and other leucocytes regularly occur within and subjacent to the gut epithelium. Recent data suggest that intestinal epithelial cells may exert accessory immunological functions. Although interactions between leucocytes and accessory cells usually require expression of adhesion molecules, intestinal epithelium has generally been considered negative for intercellular adhesion molecule-1 (ICAM-1) by immunohistochemical techniques. We therefore studied the expression of ICAM-1 and lymphocyte function-associated antigen-3 (LFA-3) by two colonic epithelial cell lines and found that both adhesion molecules were constitutively present at low levels. ICAM-1 protein expression could be enhanced within 4 h by cytokines, particularly after co-incubation with interferon-gamma (IFN) and tumour necrosis factor-alpha (TNF), interleukin-1 beta (IL-1), or IL-6. IFN also resulted in accumulation of ICAM-1 mRNA. Conversely, the LFA-3 expression was virtually unaffected by cytokine stimulation. These data imply that intestinal epithelial cells under certain conditions may bear adhesion molecules required for cooperation with juxtaposed leucocytes in situ, and that the expression of some of these molecules is modulated by cytokines from activated mucosal leucocytes.

[Symptomatic cytomegalovirus infection in patients with acquired immunodeficiency syndrome]

During a seven-year period, symptomatic cytomegalovirus (CMV)-infection was diagnosed in 21.5% (n = 10) of all AIDS patients at the National Hospital of Norway (retinitis n = 8, colitis n = 3, pneumonitis n = 2, gastritis n = 1). Symptomatic cytomegalovirus-infection was associated with a poor long-term prognosis (median survival 174 days, range 10-415). Median CD4+ lymphocyte counts at onset of symptomatic cytomegalovirus-infection was 24 x 10(6)/l (range 6-68). Regular ophthalmological examination of HIV-infected patients with severe immunodeficiency, and endoscopy with multiple mucosal biopsies in patients with suspected cytomegalovirus-infection of the gastrointestinal tract, were of major importance in diagnosing symptomatic cytomegalovirus-infection. Six patients received an induction course of ganciclovir, and foscarnet was administered in two patients due to leukopenia. Problems of toxicity to the available anti-CMV agents make the development of additional therapeutic approaches desirable.

The significance of anti-hepatitis C virus antibodies measured in chronic liver disease

The frequency of hepatitic C virus (HCV) antibodies was determined in two different laboratories in stored sera from 128 consecutive patients with chronic liver disease and from 41 healthy blood donors. Repeated measurements were performed in most patients. At the first determination the frequency of HCV antibodies was 7% in primary sclerosing cholangitis, 42% in primary biliary cirrhosis, 40% in autoimmune chronic active hepatitis, and 27% in alcoholic liver disease. The reproducibility of the determinations was rather poor, with a within-assay variation of 9.9%, whereas the between-assay variation was 34% and 47% in the two laboratories. There was a significant difference in the results obtained in the controls, depending on the handling of the sera. Freezing and thawing and, possibly, protracted storing of sera had a major impact on the assay and may have invalidated the results obtained in many studies. A significant association between IgG levels and titers of HCV antibodies was found in the total group of patients (p less than 0.005), in autoimmune chronic active hepatitis (p less than 0.005), and in primary biliary cirrhosis (p less than 0.01). It may be questioned whether the assay really is specific for anti-HCV antibodies in these patients. Whether HCV has anything to do with the etiology and pathogenesis of chronic liver disease apart from NANB-hepatitis is still undetermined.

Protein kinase C activation selectively increases mRNA levels for one of the regulatory subunits (RI alpha) of cAMP-dependent protein kinases in HT-29 cells

We have examined the effect of the protein kinase C activator, TPA, on mRNA levels for subunits of cAMP-dependent protein kinases in the human colonic cancer cell line HT-29, subline m2. Messenger RNA for the regulatory subunit, RI alpha, of cAMP-dependent protein kinases was shown to be present and regulated by TPA. Other mRNAs for subunits of cAMP-dependent protein kinases (RI beta, RII alpha, RII beta, C alpha, C beta) were also present in these cells, but revealed no or only minor changes upon TPA stimulation. When HT-29 cells were cultured in the presence of 10 nM TPA for various time periods, a biphasic response was observed in RI alpha mRNA levels with a maximal increase (approximately 4 fold) after 24 hours. TPA stimulated RI alpha mRNA increased in a concentration-dependent manner and maximal response (4-8 fold) was seen at 3-10 nM. The TPA-induced increase in RI alpha mRNA was not obtained when cells were incubated with TPA together with the protein kinase C inhibitors, staurosporine or H7. The cAMP-analog 8-CPTcAMP alone induced RI alpha mRNA levels 50% more than TPA. Combined treatment with TPA (10 nM) and 8-CPTcAMP (0.1 mM) gave an increase in RI alpha mRNA similar to TPA. These results demonstrate an interaction between the protein kinase C pathway and mRNA levels for the RI alpha subunit of cAMP-dependent protein kinases in HT-29 cells.

[New biotechnologic products in treatment and prevention]

Biotechnology will create new generations of DNA and peptide products in pharmacology. Such products may change clinical practice in the treatment of a variety of diseases, for example cancer and infectious, cardiovascular, and genetic diseases. Development of new vaccines using biotechnology may be effective in preventing or treating serious infectious diseases or cancer. We discuss approved and putative applications of biotechnological products in clinical medicine.

Rapid selection of cultured cells with increased expression of a membrane marker (secretory component)

This study showed how immunomagnetic monodisperse microspheres (Dynabeads) can be used for rapid selection of stable and homogeneous sublines of cancer cells. The beads were activated with antibody to a specific surface membrane marker. We used a monoclonal antibody (MAb) to human secretory component (SC), the epithelial receptor for polymeric immunoglobulins (pIg). A relatively low number of particles favored rosetting of strongly positive cells. SC-expressing cells were isolated within 30 min from a colonic carcinoma cell line (HT-29.E10). After 13 months of continuous culture the selected cells had a 15 times higher cellular content and a 10 times higher secretory rate of SC than parallel cultures of the original cell line. Immunomagnetic microspheres can be recommended in experimental cancer research, e.g., in order to minimize cellular heterogeneity and to isolate cells with particular surface membrane phenotypes in differentiation studies. The selection method is rapid and simple, and eliminates laborious test systems for conventional subclone screening.

Up-regulation of the expression of secretory component and HLA molecules in a human colonic cell line by tumour necrosis factor-alpha and gamma interferon

Secretory component (SC) acts as a receptor for polymeric IgA (pIgA) and pIgM on the basolateral face of secretory epithelia. This study showed that both the production and surface membrane expression of SC were additively up-regulated by tumour necrosis factor-alpha (TNF) and gamma interferon (IFN-gamma) in a human colonic cell line (HT-29m2). TNF likewise enhanced membrane expression of HLA class I determinants. Moreover, TNF augmented synergistically the IFN-induced de novo synthesis of HLA class II (DR) molecules. These data suggest that there are different regulatory mechanisms for the action of TNF and IFN and for the expression of HLA-DR and SC/HLA class I. Addition of actinomycin D abolished the cytokine-mediated increase of SC synthesis and expression. This observation suggested that transcriptional events are required for the cytokine-mediated up-regulation of SC.

Lymphoepithelial interactions in the mucosal immune system

Images

Tumor necrosis factor-alpha up-regulates expression of secretory component, the epithelial receptor for polymeric Ig

Secretory component (SC) is the receptor that facilitates transcytosis of polymeric IgA and polymeric IgM through secretory epithelial cells and into exocrine fluids. The present study showed that rTNF-alpha enhanced the cellular pool, membrane expression, and secretion of functionally SC in a human colonic carcinoma cell line (HT-29m2) which is known to express and process SC like normal glandular cells. TNF-alpha also up-regulated membrane expression of the constitutive HLA class I molecules, whereas the cells remained HLA class II-negative.

Tumor necrosis factor-alpha up-regulates expression of secretory component, the epithelial receptor for polymeric Ig

Secretory component (SC) is the receptor that facilitates transcytosis of polymeric IgA and polymeric IgM through secretory epithelial cells and into exocrine fluids. The present study showed that rTNF-alpha enhanced the cellular pool, membrane expression, and secretion of functionally SC in a human colonic carcinoma cell line (HT-29m2) which is known to express and process SC like normal glandular cells. TNF-alpha also up-regulated membrane expression of the constitutive HLA class I molecules, whereas the cells remained HLA class II-negative.

Production and secretion of immunoglobulins in the gastrointestinal tract

Two decades ago it was shown that the major immunoglobulin (Ig) present in human secretions is a dimeric IgA covalently bound to an epithelial glycoprotein of about 80 kD, now called the secretory component (SC). Pentameric IgM is likewise actively enriched in most exocrine fluids and is associated with SC, although not in a covalently stabilized complex. Three findings explain the selective translocation of polymeric Ig (pIg) into exocrine fluids: (1) preferential local production; (2) J-chain-expressing capacity of pIg-producing immunocytes; and (3) SC-mediated epithelial transport. Human hepatocytes lack SC and the human liver, therefore, cannot act as an efficient "IgA pump". This is in contrast to the rat liver which shows a remarkable capacity for transport of dimeric IgA from blood into the bile. The J chain of pIg and the epithelial SC represent the "lock and key" in the glandular transport of secretory IgA (SIgA) and SIgM. It has recently been shown that SC is synthesized as a transmembrane protein of about 95 kD and constitutes the actual pIg surface receptor. Complexing between ligand and receptor in the plasma membrane is followed by endocytosis. The completed SIgA and SIgM molecules are then translocated in cytoplasmic vesicles through the epithelial cell to the gland lumen along with an excess of free SC. The main function of SIgA is to exert immune exclusion; that is, by intimate cooperation with innate nonspecific defense factors it decreases penetration of soluble antigens and inhibits epithelial colonization of bacteria and viruses. Especially in selective IgA deficiency, SIgM may exert a similar protective function since its synthesis is markedly increased in the intestinal mucosa. Leakage of IgG into exocrine fluids is enhanced by mucosal irritation. Although IgG should not be considered as a SIg, it may contribute to immune exclusion. This is seen especially in the respiratory tract where IgG is less easily subjected to proteolytic degradation than in the intestinal juice. In contrast, by activating complement, IgG antibodies may at the same time be phlogistic and accelerate mucosal penetration of antigens. IgG may thus contribute to persistent immunopathology in mucosal disease. The same is true for IgE antibodies which may be carried into mucous membranes and secretions by mast cells and cause their degranulation with local histamine release. Traces of IgD may likewise be found in the secretions but without obvious biologic significance. Regulation of secretory immunity takes place both in organized lymphoepithelial structures, such as the Peyer's patches, and adjacent to the glands in the lamina propria.(ABSTRACT TRUNCATED AT 400 WORDS)

Early detection of liver metastasis in patients with colorectal carcinoma by increased levels of circulating IgA- and IgM-associated secretory component

One hundred patients operated for colorectal carcinoma were followed clinically and with serial blood samples from 5 to 8 years. Levels of secretory component (SC) associated with IgA and IgM in serum were measured and related to Dukes' stage, histological differentiation, tumour expression of SC, and circulating carcinoembryonic antigen (CEA). On the whole, elevated levels of SC in serum were found in 15 of the 20 patients who already had (n = 15), or later developed (n = 5), liver metastasis. Four of the latter 5 patients showed raised SC levels with a 5.5 months median lead time from the first positive serum sample to clinically manifest liver disease. These data are interesting in view of the promising results reported for liver resection in patients with colorectal carcinoma.

Interferon-gamma enhances expression of secretory component, the epithelial receptor for polymeric immunoglobulins

Recombinant interferon-gamma (IFN-gamma) increased in a dose-dependent manner the intracellular pool, the membrane expression, and the shedding of secretory component (SC) in human colonic adenocarcinoma cell line (HT-29). A similar dose-response relationship was observed when we examined the binding of polymeric IgA to HT-29 cells treated with IFN-gamma, thus reflecting expression of functional SC. Because IFN-gamma is produced by T cells during immune responses, activated T cells may be able to promote the external transport of dimeric IgA and pentameric IgM and thereby enhance the efferent limb of the secretory immune system. This is, therefore, the first observation indicating how the secretory transport capacity may be adjusted to increased local immunoglobulin production.

Interferon-gamma enhances expression of secretory component, the epithelial receptor for polymeric immunoglobulins

Recombinant interferon-gamma (IFN-gamma) increased in a dose-dependent manner the intracellular pool, the membrane expression, and the shedding of secretory component (SC) in human colonic adenocarcinoma cell line (HT-29). A similar dose-response relationship was observed when we examined the binding of polymeric IgA to HT-29 cells treated with IFN-gamma, thus reflecting expression of functional SC. Because IFN-gamma is produced by T cells during immune responses, activated T cells may be able to promote the external transport of dimeric IgA and pentameric IgM and thereby enhance the efferent limb of the secretory immune system. This is, therefore, the first observation indicating how the secretory transport capacity may be adjusted to increased local immunoglobulin production.

Circulating secretory component in breast neoplasms

The serum concentrations of IgAp and IgMr associated secretory component (SIgA and SIgM) of 98 patients with neoplasms of the breast were measured. Of the 56 patients with carcinomas, 11 had increased concentrations of circulating SIgM, which was almost twice as sensitive as SIgA as a marker for carcinoma. Concentrations of circulating SIgA and SIgM were independent of expression of secretory component, IgA, and carcinoembryonic antigen (CEA); histological tumour grade; and tumour cell DNA ploidy, whereas a weak correlation between SIgA and SIgM and circulating CEA was seen. The three patients who had liver metastases indicated had particularly high concentrations of circulating SIgA and SIgM, whereas no difference was generally seen between patients with malignancy and those with benign tumours.