Biomedical subjects

A T Vella

Publications and source records attributed to A T Vella.

26 records · Page 2Linked to original sources

PubMed1994

Schistosoma mansoni egg-primed Th0 and Th2 cells: failure to down-regulate IFN-gamma production following in vitro culture.

Schistosoma mansoni eggs induce a rapid and pronounced Th response which, based on cytokine secretion patterns, at day 3 post priming is Th0-like and at day 10 is Th2-like. To establish whether or not the day-3 cells have been programmed in vivo to develop into Th2 cells, they were cultured for 7 days to become in vitro equivalents of day-10 in vivo cells. Following this culture period, the population was approximately 75% CD4+, 22% CD8%, 6% B220+ and capable of producing IL-2, IFN-gamma, IL-4, -5 and -10 upon stimulation. This Th0-like status was confirmed by the observations that in response to mitogen IL-4 and IFN-gamma production are both CD(4+)-cell dependent and that IFN-gamma and IL-4 are produced concomitantly by single cells. These data suggest that Th0 cells persist in vivo, but are incapable of secreting IFN-gamma at day 10 due to an inhibitory factor which does not develop or is labile in vitro. This concept is supported by the surprising observation that day-10 LN cells, which are Th2-like immediately ex-vivo, rapidly gain the ability to secrete IFN-gamma following a short period of culture.

Animals↗

PubMed1993

CD4+ T-cell receptor V beta usage during the immune response to Schistosoma mansoni.

T-cell receptor V beta usage by CD4+ cells during the immune response of C57BL/6J mice to Schistosoma mansoni was examined. During acute infection, the distribution of splenic CD4+ cells utilizing V beta s 3, 5, 6, 7, 8.1/8.2, 9, and 11 was not significantly different from that in uninfected mice. Preferential V beta usage or deletion was not detected when either the primary or the memory immune response to parasite eggs was examined.

Animals↗

PubMed1992

Schistosoma mansoni eggs induce antigen-responsive CD44-hi T helper 2 cells and IL-4-secreting CD44-lo cells. Potential for T helper 2 subset differentiation is evident at the precursor level.

Schistosoma mansoni eggs are potent inducers of biased Th2-like immune responses. Using a model system where mice are immunized with isolated schistosome eggs, we demonstrate that CD44 expression, up-regulation of which has been linked to Th cell development, is increased on Th2 cells. We also investigate the functional properties of CD44-lo Th cells recovered from the overtly Th2 environment constituted by lymph nodes draining sites of egg deposition. Production of high levels of IL-4, IL-5, and IL-10 by Th cells responding to egg Ag is shown to be the property of a subpopulation expressing CD44-hi. This population of Th cells cosegregates with a blasting subpopulation expressing more IL-4R (but similar amounts of IL-2R) than Th cells from normal mice. These results indicate that mature Th2 cells responding to schistosome eggs are CD44-hi and suggest that they use IL-4 as a growth factor. In contrast, CD44-lo cells sorted from lymph node populations responding to eggs are able to produce small amounts of IL-4 and IL-2, but no IL-5 or IL-10. This is surprising, because low expression of CD44 is considered a characteristic of Th cell naivite and concomitant ability to produce only IL-2. Thus, in lymph nodes responding to schistosome eggs, potential for Th2 subset differentiation is evident within the CD44-lo precursor Th subpopulation.

Animals↗

PubMed1992

CD4+ Th2 response induced by Schistosoma mansoni eggs develops rapidly, through an early, transient, Th0-like stage.

Data from recent studies of murine schistosomiasis mansoni have indicated that certain characteristics of this infection, such as eosinophilia and elevated IgE, are due largely to the induction of Th2-like immune responses by parasite ova. The present study was designed to examine more closely the genesis and development of these skewed Th responses to schistosome eggs. Accordingly, eggs isolated from infected mice were injected s.c. into normal mice. After inoculation, draining lymph node (LN) cells were recovered, phenotyped, and tested for their ability to proliferate and secrete IL-2 and IFN-gamma (as markers of Th1 function) and IL-4, IL-5, and IL-10 (Th2 cytokines). The results show a maximal LN enlargement of 40- to 100-fold by day 3 after egg inoculation. The CD4/CD8/B cell ratio at this time is similar to that in LN from normal mice, but increases in numbers of cells expressing very low levels of MEL-14 and high levels of Pgp-1 are evident by days 3 and 10, respectively. Surprisingly, the initial detectable Ag-specific response to schistosome eggs, observed at day 1, is the production of IFN-gamma. By day 3, LN cells are capable of proliferating and making IFN-gamma plus IL-2, IL-4, IL-5, and IL-10 when stimulated with soluble egg Ag and, therefore, appear Th0-like. After 7 to 10 days, IFN-gamma production is severely depressed but the response continues to be characterized by IL-4, IL-5, IL-10, and IL-2. Depletion studies indicate that CD4 cells are the major population responsible for Ag-mediated proliferation and cytokine production. Results show that schistosome eggs are autonomous inducers of vigorous Th2-like effector responses. Further, our data, from a system that utilizes an in vivo priming step, support the contentions that skewed Th responses develop via an intermediate Th0 stage is accompanied by a loss of the MEL-14 surface marker and an increase in Pgp-1 expression.

Animals↗

PubMed1992

Evidence for polyclonal B cell activation as the mechanism for LCMV-induced autoimmune hemolytic anemia.

A docile substrain of lymphocytic choriomeningitis virus (LCMV) causes a persistent infection in adult C3HeB mice and induces a severe autoimmune hemolytic anemia (AIHA) which is maximal around three weeks post infection (PI). Evaluations of serum immunoglobulin levels of these mice demonstrated grossly elevated IgG2a levels along with increased IgG1 and IgG2b levels, suggesting that these animals also develop polyclonal B cell activation (PBA). Interestingly, LCMV-infected B10.BR mice did not demonstrate a marked hypogammaglobulinemia nor did they experience a severe hemolytic anemia. Although evaluations of the hematocrits indicated that these animals endure a mild anemia 21 days PI, a below normal reticulocyte count until day 18 PI suggests that there was a prolonged suppression in hematopoiesis. It is clear from RBC survival studies that there is not an accelerated rate of RBC elimination, as seen in infected C3H mice, demonstrating that the anemia in B10.BR mice is not due to a hemolytic process. These results imply a correlation between the development of PBA and AIHA, suggesting a cause and effect relationship.

Agammaglobulinemia↗

PubMed1991

The presence of an anti-erythrocyte autoantibody in C3HeB/FeJ mice after lymphocytic choriomeningitis virus infection.

Lymphocytic Choriomeningitis (LCM) virus, substrain Docile, causes a chronic infection in adult C3HeB/FeJ mice. The virus also induces a severe anemia which, unlike the viremia, eventually resolves. Initially, there is frank bone marrow deficit, but the anemia persists well beyond a strong erythroid compensatory response. An immune-mediated basis for the hemolytic anemia was suggested by its abrogation in cyclophosphamide-treated mice, as well as an abnormal number of spherocytes in the circulation. We now show by ELISA assay, using either anti-mouse Ig or RBC membrane ghosts as catching antigen, that unusually high quantities of antibodies can be eluted from the RBCs of virus-infected mice. Furthermore, the high transient antibody concentration correlates with the severity of the anemia. With no evidence for complement playing a role in the anemia, these data indicate that erythrophagocytosis (via macrophage FcRs) may be the mechanism for RBC elimination. The possibility of molecular mimicry (antibody cross-reactivity between LCM and RBC membrane epitopes) was considered but appeared unlikely since the RBC antibody eluates gave no signal in an LCM-specific ELISA (which showed an ever increasing serum titer of virus-specific antibody). Isotype determination of the RBC eluates revealed the following: IgG2a much greater than IgG1 greater than IgG2b greater than IgG3 greater than IgM. The precise role, if any, of LCM-virus induced polyclonal activation (most strikingly in the IgG2a subclass) has yet to be determined.

Anemia↗

PubMed1988

Ubiquitin carrier protein-catalyzed ubiquitin transfer to histones. Mechanism and specificity.

Ubiquitinated derivatives of histones H2A and H2B, in which the carboxyl terminus of ubiquitin is joined to epsilon-amino groups of specific lysine residues of each histone, occur in vivo. Certain ubiquitin carrier proteins (E2s) catalyze ubiquitin transfer to histones (Pickart, C. M., and Rose, I. A. (1985) J. Biol. Chem. 260, 1573-1581). The catalytic activities of these purified ubiquitin carrier proteins have been quantitatively characterized with purified histones, in order to determine if one or more of them exhibits specificity for H2A over other histones (H3,H4) which are not known to be ubiquitinated in vivo. The results show the following. 1) No E2 exhibits strong specificity for H2A over the other histones. 2) For a given histone, kinetics of formation of its monoubiquitinated adduct do not differ strongly among the E2s; sigmoid kinetics (nH = 2) are generally observed, with values of K 0.5 ranging from 2-6 microM. 3) E214K catalyzes primarily monoubiquitination. 4) E220K catalyzes multiple ubiquitination (up to three ubiquitin/histone) by a processive mechanism that involves joining of ubiquitin carboxyl termini to multiple histone lysine residues. 5) E235K also catalyzes processive ubiquitination, with formation of polyubiquitinated products exhibiting a lag phase. Many of the polyubiquitinated adducts produced at low histone concentration are larger than expected for monoubiquitination of every histone-lysine residue, and polyubiquitination is selectively inhibited by substitution of reductively methylated ubiquitin for ubiquitin. These results suggest that E235K uniquely catalyzes ubiquitin transfer to lysine residues of previously conjugated ubiquitin molecule(s). The implications of these results for biological mechanisms of histone ubiquitination are discussed.

Animals↗

PubMed1988

Levels of active ubiquitin carrier proteins decline during erythroid maturation.

Energy-dependent proteolysis is lost during maturation of rabbit reticulocytes to erythrocytes (Speiser, S., and Etlinger, J.D. (1982) J. Biol Chem. 257, 14122-14127), but nothing is known about the fates of individual components in the multienzyme ATP- and ubiquitin (Ub)-dependent proteolytic pathway during this process. Rabbit reticulocytes contain five low molecular weight carrier proteins (E2s) that form labile Ub adducts in the presence of Ub-activating enzyme (E1) (Pickart, C. M. and Rose, I. A. (1985) J. Biol. Chem. 260, 1573-1581). A method to estimate levels of active E2s in erythroid cells has been developed involving: 1) stepwise anion exchange fractionation of a soluble lysate; 2) addition of purified E1, MgATP, and radioiodinated Ub to the fractions followed by gel electrophoresis of the resulting E2-Ub adducts; and 3) quantitative densitometry of autoradiographs. Levels of active E2s are much lower in (rabbit) erythrocytes than in reticulocytes. Mean -fold decreases are: E235K, 6 x; E2(25K), 11 x; E2(20K), 18 x; E2(17K), not detected in erythrocytes; E2(14K), 12 x. The large decreases in levels of E2(20K) and E2(14K) are consistent with known functions of these proteins in DNA repair and Ub-dependent proteolysis, respectively. Decreases in levels of the other E2s, whose biological roles are presently unknown, suggest diminished requirements, if any, for them in erythrocyte metabolism. The analysis revealed two previously undescribed carrier proteins, one of which has a high molecular weight. Additional catalytic properties of E2(35K) and E2(14K) are reported.

Adenosine Triphosphate↗