Specific antibody responses to the variable surface glycoproteins of Trypanosoma congolense in infected cattle

Summary Sera from cattle infected with three Trypanosoma congolense clones (ILNat 2.1, ILNat 3.1 and ILRAD 588) derived from different stocks were analysed for the presence of specific antibodies against the surface glycoproteins (VSGs) of the infecting trypanosomes using the solid and liquid-phase radioimmunoassays and the neutralization of infectivity test. High levels of IgM, IgGi and IgG₂ antibodies against the VSGs of the infecting variable antigen types (VATs) as well as other VATs that arose during the course of infection were detected. In addition, 11 out of 12 infected animals showed recurrent peaks of antibody activity against the infecting trypanosomes. The recurrent peaks of antibody activity against the VSGs of the infecting organisms would suggest either a reappearance of trypanosomes of the infecting types or emergence of organisms that bear similar surface determinants. In contrast to the studies on murine trypanosomiasis, there was little or no antibody activity against 2, 4, 6-trinitrophenylated bovine serum albumin (TNP-BSA) in sera from these cattle.     

Evidence of subjects sensitized to Leishmania infantum on the French Mediterranean coast: differences in gamma interferon production between this population and visceral leishmaniasis patients

The Marseilles region is an endemic area for visceral mediterranean leishmaniasis, but although the number of dog cases, the parasite's main host, is very high, only a few people develop the disease. We looked for sensitized healthy subjects among 25 healthy individuals living in this area by studying their in vitro lymphoproliferative response to Leishmania infantum antigens and gamma interferon synthesis. We found that 65% of tested subjects were sensitized against L. infantum. We compared their cell mediated immunity to that of 13 active Kala-Azar patients and 13 controls from non-endemic areas. In patients, results showed a specific cellular immuno-deficiency in the lymphocyte response to L. infantum antigens and a global deficiency of gamma interferon production. Interestingly, the healthy individuals from the endemic area who responded to L. infantum antigens were found to produce high gamma interferon levels after L. infantum antigen stimulation. After healing, the cell mediated-immunity of the 3 patients we followed up was similar to that of the sensitized tested healthy subjects, but the former were still producing antibodies at the time of study.     

Lymphocyte, antibody and cytokine responses during concurrent infections between helminths that selectively promote T-helper-1 or T-helper-2 activity

The injuence of Trichinella spiralis on infections with Trichuris murk was studied in non-responder B10. BR mice. Mice infectedonly with T. muris were unable to expel parasites and had many adult worms 35 days later. Infection with 300 larvae of T. spiralis, given seven or 14 (but not 28) days after T. muris, enabled mice to expel up to 90% of T. muris; expulsion of T. spiralis was not altered. Concurrently infected mice produced less T. murisspecijic IgG2a antibody than mice infected with T. muris only, andshowed higher proliferative responses when spleen and mesenteric lymph node cells were cultured in vitro with T. murk antigens. When T. spiralis was present mucosal mast cells were generated in T. muris-infected mice, whereas almost no mast cells were seen with only T. muris. Lymphocytes from doubly-infected mice produced significantly more interleukin 4 and 5 (IL-4, IL-5) and significantly less interferon-gamma (IFN-y) when stimulated in vitro with Concanavalin A (Con-A) than cells from mice infected with T. murk only. These data demonstrate that BI0.BR mice, which in single infections produce a Thl response to T. muris and develop no protective immunity, can mount a protective T-helper-2 (Th2) response and expel T. murk when concurrently infected with the ‘Th2 inducing’ nematode T. spiralis.     

Protection to Fasciola hepatica in the gut mucosa of immune rats is associated with infiltrates of eosinophils,IgG1 and IgG2a antibodies around the parasites

We investigated the immune effector mechanisms that underlie protection against F. hepatica in the gut wall of immune rats, using (immuno)histochemistry. In the lamina propria of immune Wistar rats, four weeks after oral infection, frequencies of IgE-positive cells, eosinophils and mucosal mast cells were significantly increased, compared with naïve rats. These factors represent the traditional effector mechanisms against helminths. No significant differences were detected between the two groups in frequencies of IgM-, IgG2a-, IgG1- and IgA- positive cells, CD4- and CD8-positive cells, NK cells, macrophages, neutrophils or goblet cells. Upon challenge of immune rats with F. hepatica in an ex vivo gut segment, NEJs that migrated through the (sub)mucosa were coated with IgG1 and IgG2a antibodies and surrounded by eosinophils. No IgE or IgA antibodies were detected on the parasites. The onset of these immune effector responses, two h after challenge, was related to the expression of protection. These results suggest that NEJs are killed by an eosinophil-mediated cytotoxic response involving IgG antibodies. These antibodies were not produced in the intestine, but infiltrated the gut upon challenge. The observed immune effector responses were not restricted to the site where the primary infection is located, namely the small intestine, but were also detected in the large intestine. The presence of the protective immune mechanisms in two other rat strains demonstrates the pivotal importance of these responses, irrespective the genetic background of the host.     

Effect of chronic ethanol consumption on protective T-helper 1 and T-helper 2 immune responses against the parasites Leishmania major and Strongyloides stercoralis in mice

BACKGROUND: Chronic alcohol consumption has been associated with significant increases in the prevalence of infectious diseases, and it has been suggested that these increases are caused by a direct effect of ethanol on the immune response. The objective of this study was to determine whether chronic ethanol consumption would affect the development of protective immunity to Leishmania major, which is controlled by the T-helper 1 (Th1) subset of CD4 cells, and Strongyloides stercoralis, which is controlled by the Th2 subset. METHODS: Mice were fed ethanol-containing liquid diet (25% ethanol-derived calories), liquid isocaloric diet without ethanol, or solid chow and then exposed to either of the two parasites. The ability of the mice chronically consuming alcohol to eliminate the infections was determined, as were the levels of parasite-specific humoral and cellular immune responses. RESULTS: Mice chronically consuming alcohol were capable of eliminating both of these infections in a manner identical to the control mice. In addition, splenocytes from mice chronically consuming alcohol infected with L. major produced nitric oxide at the same levels as in control mice. Antibody responses were altered in a manner suggesting an increase in Th2 immunity and a decrease in Th1 immunity in the mice chronically consuming alcohol. In mice chronically consuming alcohol that were infected with S. stercoralis, eosinophils migrated to the parasite's microenvironment, and antibodies were produced at levels equivalent to those seen in control mice. CONCLUSIONS: Mice maintained on an ethanol-containing liquid diet had some alteration in their ability to produce Th1 and Th2 immune responses yet were capable of generating unimpaired protective Th1 and Th2 responses.     

Humoral responses to a secretory Onchocerca volvulus protein: differences in the pattern of antibody isotypes to recombinant Ov20/OvS1 in generalized and hyperreactive onchocerciasis

The Onchocerca volvulus secretory protein Ov20/OvS1 represents a dominant antigen expressed in the infective larvae, microfilariae and adult stages of the parasite. The humoral responses to this protein have not yet been analysed in the polar clinical and immunological forms of onchocerciasis. Analysis by ELISA of class and subclass antibodies to Ov20/OvS1 in persons with the generalized or the hyperreactive form of onchocerciasis revealed similar strong responses of IgG1, IgG4 and IgM antibody levels in both forms of onchocerciasis and significant differences were observed in the IgE and IgA antibody classes. Computation of the ratios of antibodies showed that persons with the generalized form exhibited significantly higher ratios of IgG4 to IgG1, IgG4 to IgE, and IgM to IgE than patients with the hyperreactive form. To investigate the isotype recognition of antigenic sites on Ov20/OvS1 protein, three recombinantly expressed fragments (F1-3) of Ov20/OvS1 were probed using sera which strongly reacted with intact recombinant Ov20/OvS1. Epitope(s) on F1 comprising amino acid residues 1-63 were significantly recognized by IgG1 and IgE, while IgM recognized epitopes on all three fragments. The strongest reaction of IgM occurred with epitope(s) formed by residues 108-171 (F3). In contrast, IgG4 type antibodies were not reactive with either of the three OvS1 fragments, but they reacted with intact Ov20/OvS1 protein. Generalized onchocerciasis, unable to eliminate microfilariae, and hyperreactive onchocerciasis, with a high potency to eliminate or to reduce parasite loads, can be distinguished by a distinct pattern of isotype responses to Ov20/OvS1.     

The profile of IgG1 and IgG2a antibody responses in mice exposed to Schistosoma mansoni

The segregation of IgG2a and IgG1 immunoglobulin isotypes as markers for Th1 and Th2 lymphocytes respectively, was investigated in mice exposed to normal or optimally-irradiated S. mansoni cercariae. Using a panel of ELISAs, soluble antigens from lung-stage schistosomula, adult worms, or eggs, were probed with serum samples collected at biweekly intervals. Infected mice developed increased IgG1 responsiveness to all three antigens, especially between weeks five and seven, whereas IgG2a responses were lower, particularly to egg antigens. This confirms that Th2 responses are dominant after the onset of patency in infected mice. In comparison, vaccinated mice developed lower levels of IgG1, and higher levels of IgG2a to larval and worm antigens. Thus, they had balanced expression of IgG1 and IgG2a, despite having a dominant Th1 lymphocyte population. An elevated IgG1 response to egg antigens in vaccinated mice challenged with normal parasites, occurred two weeks later than in normal mice. Mice exposed to male-only cercariae developed IgG1 and IgG2a antibodies to larval and worm antigens. However, they also had elevated IgG1 to egg antigens from week five, despite a total absence of eggs. Therefore, adult worm antigens may cross react with the egg and stimulate the switch to Th2 dominated responsiveness.     

The conversion of phenylalanine to tyrosine in man. Direct measurement by continuous intravenous tracer infusions of L-[ring-2H5]phenylalanine and L-[1-13C]tyrosine in the postabsorptive state

Steady state phenylalanine and tyrosine turnover and the rate of conversion of phenylalanine to tyrosine in vivo were determined in 6 healthy postabsorptive adult volunteers. Continuous infusions of tracer amounts of L-[ring-²H₅]phenylalanine were administered intravenously for 13–14 hr. After 9–10 hr, a priming dose followed by a continuous infusion of L-[1-¹³C]tyrosine was added and maintained, along with the [²H₅]phenylalanine infusion, for 4 hr. Venous plasma samples were obtained before the initiation of each infusion and every 30 min during the course of the combined [²H₅]phenylalanine and [¹³C]tyrosine infusion for determination of isotopic enrichments of [²H₅]phenylalanine, [¹³C]tyrosine, and [²H₄[tyrosine by gas chromatograph-mass spectrometric analysis of the N-trifluoroacetyl-, methyl ester derivatives of the amino acids. Calculated from the observed enrichments, free phenylalanine and tyrosine turnover rates were 36.1 ± 5.1 μmole · kg^?1 · h^?1 and 39.8 ± 3.5 μmole · kg^?1 · h^?1, respectively. Phenylalanine was converted to tyrosine at the rate of 5.83 ± 0.59 μmole · kg^?1 · h^?1, accounting for approximately 16% of either the phenylalanine or the tyrosine flux. The results indicate that the normal basal steady state phenylalanine hydroxylase activity in vivo in man is lower than that obtained from phenylalanine loading studies. This supports the existence of some type of substrate activation of the enzyme as reflected in the previously reported exponential relationship between phenylalanine concentration and phenylalanine hydroxylase activity in vitro. The use of continuous simultaneous infusions of tracer amounts of stable isotope-labeled phenylalanine and tyrosine provides a direct means for studying physiological regulation of phenylalanine hydroxylase activity in vivo.