Chronic delta hepatitis in haemophiliacs

The seroepidemiological profile of HBV and HDV was investigated in 640 male haemophiliacs. Twenty-seven of forty-four HBsAg carriers were anti-HDV-IgG positive, 22 were also anti-HDV-IgM positive. A markedly lower prevalence of HDV infection was found in patients with anti-HBc in the absence of HBsAg and anti-HBs (6/41). Repeated detection of anti-HDV-IgM in 5/41 individuals of this group indicates that circulating HBsAg is not an absolute prerequisite for chronic HDV infection. Overall, chronically active HDV infection was detected more frequently in quiescent than in active chronic HBV infections. Anti-HDV-IgM was not detected in the absence of anti-HDV-IgG antibodies. Anti-HDV-IgG may disappear after resolution of HDV infection, as indicated by the low prevalence (1/42) in such individuals with past HBV infection as well as by loss of anti-HDV-IgG observed in two patients.     

CTLA-4 is required for the induction of high dose oral tolerance

Mucosal and systemic administrations of high dose antigens induce long- lasting peripheral T cell tolerance. We and others have shown that high dose peripheral T cell tolerance is mediated by anergy or deletion and is preceded by T cell activation. Co-stimulatory molecules B7-1 (CD80)/B7-2 (CD86) and their counter-receptors CD28/CTLA-4 play pivotal roles in T cell activation and immune regulation. In the present study, we examined the roles of the B7 co-stimulation pathway in the generation of high dose peripheral T cell tolerance. We found that blocking B7:CD28/CTLA-4 interaction at the time of tolerance induction partially prevented T cell tolerance, whereas selective blockade of B7:CTLA-4 interaction completely abrogated peripheral T cell tolerance induced by either oral or i.p. antigens. These results suggest that CTLA-4-mediated feedback regulation plays a crucial role in the induction of high dose peripheral T cell tolerance.      

Molecular genetic characterization of XRCC4 function

XRCC4 is a generally expressed protein of 334 amino acids that is involved in the repair of DNA double-strand breaks and in V(D)J recombination, but its function is unknown. In this study, we have used a mutational approach and the yeast two-hybrid method to perform an initial characterization of this protein. We show that the XRCC4 protein is located in the nucleus. We also demonstrate that several potential phosphorylation sites are not required for XRCC4 function in a transient V(D)J recombination assay. In addition, we show that XRCC4 forms a homodimer in vivo with the homodimerization domain being located within amino acids 115-204. Finally, we define a core domain of XRCC4 that functions in V(D)J recombination and comprises amino acids 18-204. Potential functions of XRCC4 are discussed.      

Inhibition of experimental autoimmune encephalomyelitis in Lewis rats by nasal administration of encephalitogenic MBP peptides: synergistic effects of MBP 68-86 and 87-99

Induction of mucosal tolerance by inhalation of soluble peptides with defined T cell epitopes is receiving much attention as a means of specifically down-regulating pathogenic T cell reactivities in autoimmune and allergic disorders. Experimental autoimmune encephalomyelitis (EAE) induced in the Lewis rat by immunization with myelin basic protein (MBP) and Freund's adjuvant (CFA) is mediated by CD4+ T cells specific for the MBP amino acid sequences 68-86 and 87-99. To further define the principles of nasal tolerance induction, we generated three different MBP peptides (MBP 68-86, 87-99 and the non- encephalitogenic peptide 110-128), and evaluated whether their nasal administration on day -11, -10, -9, -8 and -7 prior to immunization with guinea pig MBP (gp-MBP) + CFA confers protection to Lewis rat EAE. Protection was achieved with the encephalitogenic peptides MBP 68-86 and 87-99, MBP 68-86 being more potent, but not with MBP 110-128. Neither MBP 68-86 nor 87-99 at doses used conferred complete protection to gp-MBP-induced EAE. In contrast, nasal administration of a mixture of MBP 68-86 and 87-99 completely blocked gp-MBP-induced EAE even at lower dosage compared to that being used for individual peptides. Rats tolerized with MBP 68-86 + 87-99 nasally showed decreased T cell responses to MBP reflected by lymphocyte proliferation and IFN-gamma ELISPOT assays. Rats tolerized with MBP 68-86 + 87-99 also had abrogated MBP-reactive IFN-gamma and tumor necrosis factor-alpha mRNA expression in lymph node cells compared to rats receiving MBP 110-128 nasally, while similar low levels of MBP-reactive transforming growth factor-beta and IL-4 mRNA expressing cells were observed in the two groups. Nasal administration of MBP 68-86 + 87-99 only slightly inhibited guinea pig spinal cord homogenate-induced EAE, and passive transfer of spleen mononuclear cells from MBP 68-86 + 87-99-tolerized rats did not protect naive rats from EAE. Finally, we show that nasal administration of MBP 68-86 + 87-99 can reverse ongoing EAE induced with gp-MBP, although higher doses are required compared to the dosage needed for prevention. In conclusion, nasal administration of encephalitogenic MBP peptides can induce antigen-specific T cell tolerance and confer incomplete protection to gp-MBP-induced EAE, and MBP 68-86 and 87-99 have synergistic effects. Non-regulatory mechanisms are proposed to be responsible for tolerance development after nasal peptide administration.      

IgE Fc receptor positive T, B and NK cells in patients with the hyper-IgE syndrome

Patients with the hyper-IgE syndrome have greatly elevated percentages of IgE Fc receptor (Fc epsilon R)-positive B cells, but they have less than 0.1% Fc epsilon R+ T cells (T epsilon cells) and few, if any, Fc epsilon R+ natural killer cells. They also have markedly decreased numbers of IgG receptor positive (Fc gamma R+) T cells (T gamma cells). Patients with the hyper-IgE syndrome resemble in this respect patients with severe atopic dermatitis. Since a portion of T epsilon and T gamma cells of mildly atopic patients react with monoclonal antibody OKT8, they may have a suppressor function. However, whether the low number of T epsilon cells is responsible for the high IgE serum level in hyper-IgE syndrome and atopic dermatitis patients remains to be demonstrated. Attempts to obtain a reliable assay for human IgE synthesis in vitro to investigate the function of Fc epsilon R-positive lymphocytes proved to be difficult. Even isolated B cells from atopic donors seldom produced more than twice the quantity of IgE released from cells incubated in the presence of the protein synthesis inhibitor cycloheximide.     

Interleukin 4 acts on both high- and low-density murine B cell subpopulations to induce IgE and IgG1 synthesis in vitro

Murine B cells were activated for 24 h with either lipopolysaccharide (LPS) or polyribosyl-ribitol-phosphate (PRP), followed by addition of interleukin 4 (IL-4) and the immunoglobulin isotypes secreted into the supernatant quantitated. Without IL-4, both LPS and PRP induced mainly IgM and IgG3 and no IgE secretion. Addition of IL-4 to both LPS- and PRP-activated cells decreased the IgM and IgG3 secretion and induced a large IgG1 production. In contrast to IgG1, only LPS-activated cells secreted large amounts of IgE, demonstrating that the nature of the polyclonal B cell activator also plays an important role in the IL-4 induced IgE formation. The effect of LPS and IL-4 on high- and low-density sIgM+/sIgD+ cells was also investigated. LPS and IL-4 induced IgG1 and IgE secretion by both populations. Low-density B cells from mice infected with the parasite Nippostrongylus brasiliensis formed more IgE than low-density B cells from normal mice, presumably because these mice have more in vivo preactivated B cells committed to IgE formation. The data show that IL-4 can act on both small high-density resting B cells as well as on in vivo preactivated low-density B cells to induce IgG1 and IgE secretion.