Bernhard Fleischer

CD26: a surface protease involved in T-cell activation

CD26 is a proteolytic enzyme (dipeptidylpeptidase IV) with a wide tissue distribution and a unique specificity. Recent developments indicate that CD26 is a multifunctional molecule that may have important functions in the immune system. Here, Bernhard Fleischer reviews the current knowledge of CD26 and discusses the possible functions of this molecule in T lymphocytes.

Tetracycline therapy targets intracellular bacteria in the filarial nematode Litomosoides sigmodontis and results in filarial infertility

Intracellular bacteria have been described in several species of filarial nematodes, but their relationships with, and effects on, their nematode hosts have not previously been elucidated. In this study, intracellular bacteria were observed in tissues of the rodent parasite Litomosoides sigmodontis by transmission electron microscopy and by immunohistochemistry using antiendobacterial heat shock protein-60 antisera. Molecular phylogenetic analysis of the bacterial 16S ribosomal RNA gene, isolated by PCR, showed a close relationship to the rickettsial Wolbachia endobacteria of arthropods and to other filarial intracellular bacteria. The impact of tetracycline therapy of infected rodents on L. sigmodontis development was analyzed in order to understand the role(s) these bacteria might play in filarial biology. Tetracycline therapy, when initiated with L. sigmodontis infection, eliminated the bacteria and resulted in filarial growth retardation and infertility. If initiated after microfilarial development, treatment reduced filarial fertility. Treatment with antibiotics not affecting rickettsial bacteria did not inhibit filarial development. Acanthocheilonema viteae filariae were shown to lack intracellular bacteria and to be insensitive to tetracycline. These results suggest a mutualistic interaction between the intracellular bacteria and the filarial nematode. Investigation of such a mutualism in endobacteria-containing human filariae is warranted for a potential chemotherapeutic exploitation.

Endosymbiotic bacteria in worms as targets for a novel chemotherapy in filariasis

Endosymbiotic bacteria living in plasmodia or worm parasites are required for the homoeostasis of their host and should be excellent targets for chemotherapy of certain parasitic diseases. We show that targeting of Wolbachia spp bacteria in Onchocerca volvulus filariae by doxycycline leads to sterility of adult worms to an extent not seen with drugs used against onchocerciasis, a leading cause of blindness in African countries.

Depletion of wolbachia endobacteria in Onchocerca volvulus by doxycycline and microfilaridermia after ivermectin treatment

Ivermectin is the drug used for mass chemotherapy of onchocerciasis within the WHO African Programme for Onchocerciasis Control. This approach aims to eliminate the disease as a public health problem but using one dose per year may not completely interrupt transmission since it does not suppress microfilaridermia thoroughly enough. Here we show that additional treatment with doxycycline, previously shown to sterilise adult female worms for a few months by depletion of symbiotic wolbachia endobacteria, significantly enhances ivermectin-induced suppression of microfilaridermia, rendering anti-wolbachia treatment a promising basis for blocking transmission by a drug-based approach.

Antigen-specific T regulatory-1 cells are associated with immunosuppression in a chronic helminth infection (onchocerciasis).

Different mechanisms underlie the phenomenon of peripheral tolerance. Recently, a new subset of CD4+ T cells, called T regulatory-1 (Tr1) cells, was described which show suppressor functions in vitro and in vivo and are characterized by a predominant production of IL-10 and/or TGF-beta. Tr1 cells have so far been generated experimentally in an IL-10-rich environment and hold promise for exploitation in the suppression of alloreactions and inflammatory or allergic dispositions. However, these cells have not been characterized in infectious diseases. Here we show that in the chronic helminth infection onchocerciasis (river blindness), where patients have relatively little sign of dermatitis despite the presence of millions of small worms in the skin, T cells can be obtained which bear characteristics of Tr1 cells, producing no IL-2 or IL-4 but substantial amounts of IL-10, variable amounts of IL-5, and some IFN-gamma. These cells display elevated amounts of CTLA-4 after stimulation and are able to inhibit other T cells in coculture, in contrast to Th1 and Th2 clones. This is the first time that this type of suppressor T cell has been cloned as naturally occurring during an infectious disease.

Mycobacterium ulcerans disease

Mycobacterium ulcerans disease (Buruli ulcer) is an important health problem in several west African countries. It is prevalent in scattered foci around the world, predominantly in riverine areas with a humid, hot climate. We review the epidemiology, bacteriology, transmission, immunology, pathology, diagnosis and treatment of infections. M. ulcerans is an ubiquitous micro-organism and is harboured by fish, snails, and water insects. The mode of transmission is unknown. Lesions are most common on exposed parts of the body, particularly on the limbs. Spontaneous healing may occur. Many patients in endemic areas present late with advanced, severe lesions. BCG vaccination yields a limited, relatively short-lived, immune protection. Recommended treatment consists of surgical debridement, followed by skin grafting if necessary. Many patients have functional limitations after healing. Better understanding of disease transmission and pathogenesis is needed for improved control and prevention of Buruli ulcer.

Dipeptidyl‐peptidase IV/CD26 on T cells: analysis of an alternative T‐cell activation pathway

Summary: CD26 is a proteolytic enzyme (dipeptidyl‐peptidase IV) with a wide tissue distribution and a unique specificity that was already described 27 years ago. CD26 is expressed on a fraction of resting T cells at low density but is strongly upregulated following T‐cell activation. Recent results indicate that CD 2 6 is a muitifunctional molecule that may have important functions on T cells and in the immune system. It is associated with molecules of immunological importance such as the protein tyrosine phosphatase CD45 and adenosine deaminase (ADA) on the cell surface. Synthetic inhibitors of the enzymatic activity of CD26 have been shown to suppress certain immune reactions in vitro and in vivo. An interesting feature of CD26 is its ability to transmit a transmembrane signal to trigger functional programs in T cells. This triggering requires crosslinking of CD26 on a cell membrane. The enzymatic activity of CD2 6 is not obligatory for the activation of T cells via CD26. Since CD26 is a type II membrane protein with only six intracellular amino acids, it must deliver its signal via a signal‐transducing molecule. Signaling is dependent on the expression of the T‐cell receptor (TCR) complex with a special need for a functional ζ‐chain. In this context the ζ‐chain of the TCR complex is required for CD26‐mediated signaling but, in contrast to other co‐stimulatory molecules such as the CD2 molecule, is not sufficient for triggering the T cell.

Reactivity of infiltrating T lymphocytes with microbial antigens in Crohn's disease

Intestinal T lymphocytes are normally unresponsive to microbial and recall antigens in vitro, whereas the same antigens induce strong immune responses in peripheral-blood-derived T cells. We obtained T lymphocytes from peripheral blood and from the non-inflamed and inflamed intestinal mucosa of 6 patients (3 male, 3 female; mean age 33 years) with Crohns disease. The T cells were stimulated in vitro with a range of microbial antigens. Whereas T cells from normal mucosa were unresponsive, those from inflamed mucosa had a proliferative response comparable to that of the peripheral-blood-derived T cells. These findings suggest that physiologic unresponsiveness to luminal antigens is abrogated in the inflammatory lesions of Crohns disease patients. Infiltrating T lymphocytes may therefore mediate chronic inflammation on encountering the many antigens present in the intestine.

Congenital Transmission of Visceral Leishmaniasis (Kala Azar) From an Asymptomatic Mother to Her Child

In this article, we report the case of a 16-month-old German boy who was admitted to the Childrens Hospital of Stuttgart with a 4-week history of intermittent fever, decreased appetite, weakness, fatigue, and difficulty sleeping. He was healthy at birth and remained so for the first 15 months of his life. On admission, physical examination showed enlarged cervical, axillary, and inguinal lymph nodes, as well as hepatosplenomegaly. Laboratory data revealed pancytopenia, elevated liver function tests, and hypergammaglobulinemia. Blood, stool, and urine culture results were negative. Viral infections and rheumatologic and autoimmune disorders were ruled out, but a positive titer for Leishmaniaantibodies was noted. In a liver and bone marrow biopsy, the amastigote form of the parasite could not be seen in cells. The promastigote form of Leishmania was found and the diagnosis of visceral leishmaniasis was made by combining the cultures of both the liver and the bone marrow biopsy material in 5 mL 0.9% saline on brain heart infusion agar, supplemented with defibrinated rabbit blood and incubated at 25 to 26°C for 5 days. The parasite was identified by Southern blot analysis as Leishmania infantum. Specific therapy with the antimonial compound sodium stibogluconate with a dose of 20 mg/kg body weight was begun immediately. Within 4 days, the patient became afebrile. The side effects of treatment, including erosive gastritis, cholelithiasis, worsening hepatosplenomegaly, elevation of liver enzymes, pancreatitis, and electrocardiogram abnormalities, necessitated the discontinuation of treatment after 17 days. On discharge 4 weeks later, the patient was stabilized and afebrile with a normal spleen, normal complete blood count, normal gammaglobulins, and decreasing antibody titers toLeishmania. During the next 24 months, the patient experienced intermittent episodes of abdominal pain, decreased appetite, recurrent arthralgia, and myalgia. But at his last examination in January 1998, he was well; all symptoms mentioned above had disappeared. Because the child had never left Germany, nonvector transmission was suspected and household contacts were examined. His mother was the only one who had a positive antibody titer against Leishmania donovani complex. She had traveled several times to endemic Mediterranean areas (Portugal, Malta, and Corse) before giving birth to the boy. But she had never been symptomatic for visceral leishmaniasis. Her bone marrow, spleen, and liver biopsy results were within normal limits. Culture results and polymerase chain reaction of this material were negative. A Montenegro skin test result was positive, indicating a previous infection with Leishmania. Western blot analysis showed specific recognition by maternal antibodies of antigens of Leishmania cultured from the boys tissue. Visceral leishmaniasis is endemic to several tropical and subtropical countries, but also to the Mediterranean region. It is transmitted by the sand fly (Phlebotomus, Lutzomyia). Occasional nonvector transmissions also have been reported through blood transfusions, sexual intercourse, organ transplants, excrements of dogs, and sporadically outside endemic areas. Only 8 cases of congenital acquired disease have been described before 1995, when our case occurred. In our patient, additional evaluation showed that the asymptomatic mother must have had a subclinical infection withLeishmania that was reactivated by pregnancy, and then congenitally transmitted to the child. Visceral leishmaniasis has to be considered in children with fever, pancytopenia, and splenomegaly, even if the child has not been to an endemic area and even if there is no evidence of the disease in his environment, because leishmaniasis can be transmitted congenitally from an asymptomatic mother to her child.

ISOLATION OF PROCESSED, H-2KB-BINDING OVALBUMIN-DERIVED PEPTIDES ASSOCIATED WITH THE STRESS PROTEINS HSP70 AND GP96

Stress‐induced proteins or heat shock proteins (HSP) of 96 kDa mass (gp96) and 70 kDa mass (HSP70) have been shown previously to elicit specific immunity to tumors from which they are isolated. This immunity is dependent on CD8+ cytotoxic T cells which are readily primed in vivo by immunization with HSP. The immunization capacity of HSP relies on their ability to bind antigenic peptides. Here we show that HSP70 and gp96 preparations purified from the ovalbumin (OVA)‐transfected cell line E.G7 are associated with processed H‐2Kb ‐binding peptides which contain the major H‐2Kb ‐associated epitope SIINFEKL (OVA257 –264). Our data show for the first time in the well‐defined OVA antigen system that not only endoplasmic reticulum‐resident HSP, like gp96, are associated with processed antigenic peptides but that also the cytosolic HSP70 protein forms complexes with major finally processed MHC‐binding epitopes.