Lysis mediated by T cells and restricted by H-2 antigen of target cells infected with vaccinia virus

VARIOUS virus infections lead to the formation of cytotoxic lymphocytes (CL), which are capable of killing virus-infected target cells1−4. Specific lysis of target cells infected with 51Cr-labelled vaccinia virus could be observed when investigating the cell-mediated cytotoxic reaction to vaccinia virus5; the CL could be characterised as a T cell. The sensitised lymphocytes from C3H mice could only kill syngeneic L929 cells infected with vaccinia virus, whereas lysis by sensitised lymphocytes derived from DBA/2 mice was restricted to the syngeneic infected mastocytoma P815X2 cells. In the lymphocytic choriomeningitis infection the target cell lysis was shown to be restricted by H-2 antigen6. We report here experiments with primary fibroblasts of the mouse strains C3H, DBA/2 and the (C3H DBA/2)F1 generation were designed to affirm that the effector phase of virus-specific lysis of target cells mediated by T cells is restricted by H-2 antigen even in the vaccinia virus infection. Further experiments with H-2 alloantisera were performed to indicate the close local relationship between H-2 antigens and viral surface antigens

Population studies on Phytophthora infestans on potatoes and tomatoes in southern Germany

Fifty-seven isolates of Phytophthora infestans from blighted potato foliage were collected in 1995 in southern Germany and analysed for mating type and sensitivity to metalaxyl. Fifty-six of them were characterised as A1 and one as A2 mating types. Resistance to metalaxyl was observed frequently: 53 isolates were resistant, three were partially sensitive, and one was sensitive. In a subsequent field study in 1999, 84 isolates collected from blighted potato and tomato foliage were analysed for mating type. Seventy-two were characterised as A1 and twelve as A2 mating types. The response of 76 isolates to metalaxyl and to propamocarb was tested. The majority (42) of the 76 isolates was classified as resistant to metalaxyl; 31 were partially sensitive and only three isolates were sensitive. The results with propamocarb were less discrete; 10 isolates were classified as resistant and three were clearly sensitive. AFLP fingerprinting was used to examine the genetic structure of the southern German P. infestans population collected in 1999 and indicated that the tested population can be sub-divided into a tomato group, a potato group and a mixed group containing isolates collected from both crops. The presence of Ia and IIa mitochondrial DNA haplotypes indicates that the German P. infestans isolates belong to the new pathogen population that has also been reported in neighbouring regions of Europe. The present study indicates that at the beginning of the season only a few genotypes were present, and the population became genetically more variable at the end of the growing season

ON THE ROLE OF VIRUSES IN THE EVOLUTION OF IMMUNE RESPONSES

Mutual influences of viruses on the immune system and vice versa which lead to a biological balance are considered, with clinical and/or experimental findings. Numbers and turnover of immune cells can be correlated with numbers and growth rate of viruses; certain viruses apparently have adapted to systemic or local immune effector mechanisms. The biological balance of viruses and immune system guarentees overall protection of both host and parasite. It alos may lead to conditions where immune protective mechanisms causes cell and tissue damage leading to disease. Immunologically mediated disease may be influenced by immune regulation via HLA antigen and may therefore explain HLA-disease associations. Finally, the different specificities of antibodies vs. T Cells and the differing kinetics of their immunological memory are outlined and correlated with immune escape, immune protection and the resulting possible evolutionary pressures on viruse

Fusion of Sendai virus with the target cell membrane is required for T cell cytotoxicity

INFECTION of mice with viruses can generate cytotoxic T lymphocytes (CTL) which show restricted specificity for target cell lysis. Specific lysis requires that the virus used to prime the target cells must be of the same type as that used to sensitise the CTL, and that both target and CTL cells must express the same major histocompatability complex (MHC) gene product(s). The nature of the viral gene product(s) and their interaction with the MHC gene product(s) have been the subject of recent stud1−5. Previously we used Sendai virus to show that lysable target cells can be obtained using membrane vesicles which contain only the viral glycoproteins, indicating that these may be the specific viral gene products involved in target formation5. Sendai virus contains two glycoproteins—the haemagglutinin-neuraminidase (HANA) which promotes attachment of virus to cells and the fusion protein (F) which is involved in subsequent virus cell fusion7−9. Both activities are necessary for insertion of these viral glycoproteins into the plasma membrane of the cell10. In this letter we suggest that the insertion of the viral glycoproteins into the cell membrane is an essential step in target cell formation since we can show that virus containing an inactive fusion protein precursor (F0) cannot elicit T cell cytotoxicity unless the fusion activity is generated by proteolytic cleavage of the precursor. Sugamura et al. 6 have suggested that it is primarily the F glycoprotein of the Sendai virus envelope which is essential for the formation of the target antigen, as virus lacking the functional activities of F following trypsin digestion was inactive in priming target cells for T cell killing. However, we show that proteolytic inactivation of either of the two glycoproteins (F or HANA) of virus used to prime target cells will abolish the cytotoxic response

On the physical basis of cosmic time

In this manuscript we initiate a systematic examination of the physical basis for the time concept in cosmology. We discuss and defend the idea that the physical basis of the time concept is necessarily related to physical processes which could conceivably take place among the material constituents available in the universe. It is common practice to link the concept of cosmic time with a space-time metric set up to describe the universe at large scales, and then define a cosmic time $t$ as what is measured by a comoving standard clock. We want to examine, however, the physical basis for setting up a comoving reference frame and, in particular, what could be meant by a standard clock. For this purpose we introduce the concept of a `core' of a clock (which, for a standard clock in cosmology, is a scale-setting physical process) and we ask if such a core can--in principle--be found in the available physics contemplated in the various `stages' of the early universe. We find that a first problem arises above the quark-gluon phase transition (which roughly occurs when the cosmological model is extrapolated back to $\sim 10^{-5}$ seconds) where there might be no bound systems left, and the concept of a physical length scale to a certain extent disappears. A more serious problem appears above the electroweak phase transition believed to occur at $\sim 10^{-11}$ seconds. At this point the property of mass (almost) disappears and it becomes difficult to identify a physical basis for concepts like length scale, energy scale and temperature -- which are all intimately linked to the concept of time in modern cosmology. This situation suggests that the concept of a time scale in `very early' universe cosmology lacks a physical basis or, at least, that the time scale will have to be based on speculative new physics.Comment: 44 pages. Submitted to Studies in History and Philosophy of Modern Physic

Neonatal tolerance to Mls-1a determinants: deletion or anergy of Vβ6 + T lymphocytes depending upon MHC compatibility of neonatally injected cells

Recent investigations in mice revealed that natural immunologlcal tolerance to endogenous minor lymphocyte-stimulating locus 1a (MIs-1a antigen correlates primarily with deletion of Mls-1aspeciflc Vβ6+ T lymphocytes In the thymus. Similar mechanisms account for acquired tolerance in some Instancessince the neonatal injection of Mls-1 a-expressing MHC compatible cells in neonatal mice within the first 24 hof life causes clonal deletion of Vβ6+ T cells. Here we demonstrate that Vβ6+ T cells are not deleted In mice neonatally treated with Mls-1a spleen cells expressing allogenelc H-2 molecules. However, when such non-deleted Vβ6+ T cells were tested In vitro, no interleukin 2 (IL-2) secretion or proliferation was observed after Mls-1a stimulation. This non-responsive state could be overcome by addition of exogenous IL-2, consistent with the fact that Vβ6+ cells enlarged and expressed IL-2 receptors upon Mls-1a stimulation. Furthermore, the same neonatally treated mice showed In vitro functional unresponsiveness of cytotoxic T cells but not of IL-2-secreting cells specific for the tolerated allogeneic MHC antigens. Taken together, our data Indicate that neonatal tolerance to Mls-1a can be accomplished by either clonal deletion or clonal anergy, and that it does not necessarily correlate with tolerance to MHC determinant

Altered serological and cellular reactivity to H-2 antigens after target cell infection with vaccinia virus

MICE generate cytotoxic T lymphocytes (CTL) which are able to lyse virus infected target cells in vitro after infection with lymphocytic choriomeningitis virus (LCMV) and pox-viruses1−3. CTL kill syngeneic and semiallogenic infected cells but not allogenic infected targets. Target cell lysis in these systems seems to be restricted by H-2 antigens, especially by the K or D end of the major histocompatibility complex (MHC). In experiments where virus specific sensitised lymphocytes kill virus infected allogenic target cells4 the effector lymphocytes have not been characterised exactly. Recent investigations suggest that the active cell in this assay, at least in the measles infection, is a non-thymus derived cell (H. Kreth, personal communication). An H-2 restriction of cell mediated cytolysis (CMC) to trinitrophenol (TNP)-modified lymphocytes has also been described5. Zinkernagel and Doherty6 postulated that the CTL is directed against syngeneic H-2 antigens and viral antigens and they suggested an alteration of H-2 induced by the LCMV infection. Earlier7 we found a close topological relationship between H-2 antigens and the target antigen(s) responsible for CMC in the vaccinia system. Here we report experiments which were carried out to prove alteration of H-2 after infection of L-929 fibroblasts with vaccinia virus

Involvement of Mhc Loci in immune responses that are not Ir-gene-controlled

Twenty-nine randomly chosen, soluble antigens, many of them highly complex, were used to immunize mice of two strains, C3H and B10.RIII. Lymphnode cells from the immunized mice were restimulated in vitro with the priming antigens and the proliferative response of the cells was determined. Both strains were responders to 28 of 29 antigens. Eight antigens were then used to immunize 11 congenic strains carrying different H-2 haplotypes, and the T-cell proliferative responses of these strains were determined. Again, all the strains responded to seven of the eight antigens. These experiments were then repeated, but this time -antibodies specific for the A (AA) or E (EE) molecules were added to the culture to block the in vitro responsiveness. In all but one of the responses, inhibition with both A-specific and E-specific antibodies was observed. The response to one antigen (Blastoinyces) was exceptional in that some strains were nonresponders to this antigen. Furthermore, the response in the responder strains was blocked with A-specific, but not with E-specific, antibodies. The study demonstrates that responses to antigens not controlled by Irr genes nevertheless require participation of class II Mhc molecules. In contrast to Ir gene-controlled responses involving either the A- or the E-molecule controlling loci (but never both), the responses not Ir-controlled involve participation of both A- and E-controlling loci. The lack of Ir-gene control is probably the result of complexity of the responses to multiple determinants. There is thus no principal difference between responses controlled and those not controlled by Ir genes: both types involve the recognition of the antigen, in the context of Mhc molecules

A pentapeptide as minimal antigenic determinant for MHC class I-restricted T lymphocytes

Peptides that are antigenic for T lymphocytes are ligands for two receptors, the class I or II glycoproteins that are encoded by genes in the major histocompatibility complex, and the idiotypic / chain T-cell antigen receptor1–9. That a peptide must bind to an MHC molecule to interact with a T-cell antigen receptor is the molecular basis of the MHC restriction of antigen-recognition by T lymphocytes10,11. In such a trimolecular interaction the amino-acid sequence of the peptide must specify the contact with both receptors: agretope residues bind to the MHC receptor and epitope residues bind to the T-cell antigen receptor12,13. From a compilation of known antigenic peptides, two algorithms have been proposed to predict antigenic sites in proteins. One algorithm uses linear motifs in the sequence14, whereas the other considers peptide conformation and predicts antigenicity for amphipathic -helices15,16. We report here that a systematic delimitation of an antigenic site precisely identifies a predicted pentapeptide motif as the minimal antigenic determinant presented by a class I MHC molecule and recognized by a cytolytic T lymphocyte clone