Zebrafish Embryo Infection Model to Investigate Pseudomonas aeruginosa Interaction With Innate Immunity and Validate New Therapeutics

The opportunistic human pathogen Pseudomonas aeruginosa is responsible for a variety of acute infections and is a major cause of mortality in chronically infected patients with cystic fibrosis (CF). Considering the intrinsic and acquired resistance of P. aeruginosa to currently used antibiotics, new therapeutic strategies against this pathogen are urgently needed. Whereas virulence factors of P. aeruginosa are well characterized, the interplay between P. aeruginosa and the innate immune response during infection remains unclear. Zebrafish embryo is now firmly established as a potent vertebrate model for the study of infectious human diseases, due to strong similarities of its innate immune system with that of humans and the unprecedented possibilities of non-invasive real-time imaging. This model has been successfully developed to investigate the contribution of bacterial and host factors involved in P. aeruginosa pathogenesis, as well as rapidly assess the efficacy of anti-Pseudomonas molecules. Importantly, zebrafish embryo appears as the state-of-the-art model to address in vivo the contribution of innate immunity in the outcome of P. aeruginosa infection. Of interest, is the finding that the zebrafish encodes a CFTR channel closely related to human CFTR, which allowed to develop a model to address P. aeruginosa pathogenesis, innate immune response, and treatment evaluation in a CF context.

Impact of UV Radiation on the Raman Signal of Cystine: Implications for the Detection of S-rich Organics on Mars

Traces of life may have been preserved in ancient martian rocks in the form of molecular fossils. Yet the surface of Mars is continuously exposed to intense UV radiation detrimental to the preservation of organics. Because the payload of the next rovers going to Mars to seek traces of life will comprise Raman spectroscopy tools, laboratory simulations that document the effect of UV radiation on the Raman signal of organics appear critically needed. The experiments conducted here evidence that UV radiation is directly responsible for the increase of disorder and for the creation of electronic defects and radicals within the molecular structure of S-rich organics such as cystine, enhancing the contribution of light diffusion processes to the Raman signal. The present results suggest that long exposure to UV radiation would ultimately be responsible for the total degradation of the Raman signal of cystine. Yet because the degradation induced by UV is not instantaneous, it should be possible to detect freshly excavated S-rich organics with the Raman instruments on board the rovers. Alternatively, given the very short lifetime of organic fluorescence (nanoseconds) compared to most mineral luminescence (micro- to milliseconds), exploiting fluorescence signals might allow the detection of S-rich organics on Mars. In any case, as illustrated here, we should not expect to detect pristine S-rich organic compounds on Mars, but rather by-products of their degradation.

Bacterial behavior in human blood reveals complement evaders with some persister-like features

Bacterial bloodstream infections (BSI) are a major health concern and can cause up to 40% mortality. Pseudomonas aeruginosa BSI is often of nosocomial origin and is associated with a particularly poor prognosis. The mechanism of bacterial persistence in blood is still largely unknown. Here, we analyzed the behavior of a cohort of clinical and laboratory Pseudomonas aeruginosa strains in human blood. In this specific environment, complement was the main defensive mechanism, acting either by direct bacterial lysis or by opsonophagocytosis, which required recognition by immune cells. We found highly variable survival rates for different strains in blood, whatever their origin, serotype, or the nature of their secreted toxins (ExoS, ExoU or ExlA) and despite their detection by immune cells. We identified and characterized a complement-tolerant subpopulation of bacterial cells that we named “evaders”. Evaders shared some features with bacterial persisters, which tolerate antibiotic treatment. Notably, in bi-phasic killing curves, the evaders represented 0.1–0.001% of the initial bacterial load and displayed transient tolerance. However, the evaders are not dormant and require active metabolism to persist in blood. We detected the evaders for five other major human pathogens: Acinetobacter baumannii, Burkholderia multivorans, enteroaggregative Escherichia coli, Klebsiella pneumoniae, and Yersinia enterocolitica. Thus, the evaders could allow the pathogen to persist within the bloodstream, and may be the cause of fatal bacteremia or dissemination, in particular in the absence of effective antibiotic treatments.

Blood infections by antibiotic resistant bacteria, notably Pseudomonas aeruginosa, are major concerns in hospital settings. The complex interplay between P. aeruginosa and the innate immune system in the context of human blood is still poorly understood. By studying the behavior of various P. aeruginosa strains in human whole blood and plasma, we showed that bacterial strains display different rate of tolerance to the complement system. Despite the complement microbicide activity, most bacteria withstand elimination through phenotypic heterogeneity creating a tiny (<0.1%) subpopulation of transiently tolerant evaders able to persist in plasma. This phenotypic heterogeneity thus prevents total elimination of the pathogen from the circulation, and represents a new strategy to disseminate within the organism.

Inflammasome activation by Pseudomonas aeruginosa's ExlA pore-forming toxin is detrimental for the host

During acute Pseudomonas aeruginosa infection, the inflammatory response is essential for bacterial clearance. Neutrophil recruitment can be initiated following the assembly of an inflammasome within sentinel macrophages, leading to activation of caspase-1, which in turn triggers macrophage pyroptosis and IL-1β/IL-18 maturation. Inflammasome formation can be induced by a number of bacterial determinants, including Type III secretion systems (T3SSs) or pore-forming toxins, or, alternatively, by lipopolysaccharide (LPS) via caspase-11 activation. Surprisingly, previous studies indicated that a T3SS-induced inflammasome increased pathogenicity in mouse models of P. aeruginosa infection. Here, we investigated the immune reaction of mice infected with a T3SS-negative P. aeruginosa strain (IHMA879472). Virulence of this strain relies on ExlA, a secreted pore-forming toxin. IHMA879472 promoted massive neutrophil infiltration in infected lungs, owing to efficient priming of toll-like receptors, and thus enhanced the expression of inflammatory proteins including pro-IL-1β and TNF-α. However, mature-IL-1β and IL-18 were undetectable in wild-type mice, suggesting that ExlA failed to effectively activate caspase-1. Nevertheless, caspase-1/11 deficiency improved survival following infection with IHMA879472, as previously described for T3SS+ bacteria. We conclude that the detrimental effect associated with the ExlA-induced inflammasome is probably not due to hyperinflammation, rather it stems from another inflammasome-dependent process.

Burial-induced oxygen-isotope re-equilibration of fossil foraminifera explains ocean paleotemperature paradoxes

Oxygen-isotope compositions of fossilised planktonic and benthic foraminifera tests are used as proxies for surface- and deep-ocean paleotemperatures, providing a continuous benthic record for the past 115 Ma. However, visually imperceptible processes can alter these proxies during sediment burial. Here, we investigate the diffusion-controlled re-equilibration process with experiments exposing foraminifera tests to elevated pressures and temperatures in isotopically heavy artificial seawater (H₂¹⁸O), followed by scanning electron microscopy and quantitative NanoSIMS imaging: oxygen-isotope compositions changed heterogeneously at submicrometer length scales without any observable modifications of the test ultrastructures. In parallel, numerical modelling of diffusion during burial shows that oxygen-isotope re-equilibration of fossil foraminifera tests can cause significant overestimations of ocean paleotemperatures on a time scale of 10⁷ years under natural conditions. Our results suggest that the late Cretaceous and Paleogene deep-ocean and high-latitude surface-ocean temperatures were significantly lower than is generally accepted, thereby explaining the paradox of the low equator-to-pole surface-ocean thermal gradient inferred for these periods.

The oxygen-isotope composition of fossil foraminifera tests is an established proxy for ocean paleotemperatures. Here, the authors show that isotope re-equilibration can occur during sediment burial without structural modification of the tests and cause a substantial overestimation of ocean paleotemperatures.

Origin and age of the earliest Martian crust from meteorite NWA 7533

The ancient cratered terrain of the southern highlands of Mars is thought to hold clues to the planet's early differentiation, but until now no meteoritic regolith breccias have been recovered from Mars. Here we show that the meteorite Northwest Africa (NWA) 7533 (paired with meteorite NWA 7034) is a polymict breccia consisting of a fine-grained interclast matrix containing clasts of igneous-textured rocks and fine-grained clast-laden impact melt rocks. High abundances of meteoritic siderophiles (for example nickel and iridium) found throughout the rock reach a level in the fine-grained portions equivalent to 5 per cent CI chondritic input, which is comparable to the highest levels found in lunar breccias. Furthermore, analyses of three leucocratic monzonite clasts show a correlation between nickel, iridium and magnesium consistent with differentiation from impact melts. Compositionally, all the fine-grained material is alkalic basalt, chemically identical (except for sulphur, chlorine and zinc) to soils from Gusev crater. Thus, we propose that NWA 7533 is a Martian regolith breccia. It contains zircons for which we measured an age of 4,428 ± 25 million years, which were later disturbed 1,712 ± 85 million years ago. This evidence for early crustal differentiation implies that the Martian crust, and its volatile inventory, formed in about the first 100 million years of Martian history, coeval with earliest crust formation on the Moon and the Earth. In addition, incompatible element abundances in clast-laden impact melt rocks and interclast matrix provide a geochemical estimate of the average thickness of the Martian crust (50 kilometres) comparable to that estimated geophysically.

Disseminated toxoplasmosis in a Mediterranean pregnant Risso's dolphin (Grampus griseus) with transplacental fetal infection

Fatal disseminated toxoplasmosis was diagnosed in a Risso's dolphin (Grampus griseus) dam and its fetus on the basis of pathologic findings, immunohistochemistry, and structure of the parasite. The dolphin was stranded alive on the Spanish Mediterranean coast and died a few hours later. At necropsy the dam was in good condition. From the standpoint of pathology, however, it had generalized lymphadenomegaly and splenomegaly, enlargement of and multifocal hemorrhage in the adrenal glands, diffuse mucosal hemorrhage of the glandular and pyloric stomach, ulcerative glossitis and stomatitis, focal erosions and reddening of the laryngeal appendix, and severe paraotic sinusitis with intralesional nematodes Crassicauda grampicola. The dolphin was pregnant, most probably in the first gestational trimester. The most prominent microscopic lesions were multifocal granulomatous encephalomyelitis, diffuse subacute interstitial pneumonia, mild multifocal necrotizing hepatitis and nonsuppurative cholangiohepatitis, gastritis and adrenalitis, mild lymphoid depletion, medullary sinus and follicular histyocitosis, and systemic hemosiderosis. The fetus had foci of coagulative and lytic necrosis in the kidneys, the lung, and the heart. Most lesions were associated with tachyzoites and tissue cysts of Toxoplasma gondii. The diagnosis was confirmed immunohistochemically. This is the first report on toxoplasmosis in a Risso's dolphin (G. griseus) and on transplacental transmission to an early-stage fetus in any cetaceans.

Cutaneous hyalohyphomycosis caused by Fusarium solani in a loggerhead sea turtle (Caretta caretta L.)

Fusarium solani was reported as the agent of a cutaneous infection in an injured sea turtle collected in the Mediterranean Sea. The turtle was treated with both a topical 10% solution of iodine in alcohol and ketoconazole. The source of the causal agent was traced to the sand in the tank in which the turtle was maintained. The strain was only sensitive in vitro to amphotericin B and was resistant to 5-fluorocytosine, fluconazole, itraconazole, and ketoconazole.

Correlation between invariant chain expression level and capability to present antigen to MHC class II-restricted T cells

In this study we investigated the role of the invariant chain (li) in the presentation of hen egg lysozyme (HEL) and measles virus hemagglutinin (HA) antigens to MHC class II-restricted T hybridoma cells. Fibroblastic cells transfected with Ed or Ak genes, and supertransfected or not with the li gene, were used as antigen-presenting cells (APC). For every APC pair analysed, the amount of exogenous antigen needed to obtain a T-cell response was inversely correlated with the level of li expression. Exogenously provided HEL was efficiently presented by li-supertransfected APC at doses of 10 micrograms/ml or below. In contrast, non-li transfected fibroblastic cells, which express a low level of endogenous li, required at least 10 times more HEL to stimulate most of the T hybridoma cells. Analogous results were also obtained using exogenous HA. Finally, two different experiments suggest that basal li expressed in fibroblastic cells is involved in the presentation of exogenous antigen. In the first one, we showed that li/class II ratio was increased in high-density grown fibroblastic cells and that this increase correlates with the ability of the cells to present exogenous antigen. In the second, treating high-density grown cells with an antisense li oligodeoxynucleotide could impair their ability to present exogenous HEL. We also examined the presentation of endogenously-synthesized HEL or HA after introduction of the antigen into the biosynthetic pathway of the APC by transfection of HEL and HA cDNAs. There was no apparent difference in the capability of high density grown fibroblastic cells, transfected or not with li gene, to present endogenous HEL or HA.(ABSTRACT TRUNCATED AT 250 WORDS)

T cell activation: distinct pathways involve phosphorylation of different cellular proteins

The murine T cell clone D10.G4.1 can be induced to proliferate by monoclonal antibodies (mAb) to the T cell receptor (TcR) or to Thy-1 molecules. When cells were stimulated by anti-TcR mAb, a group of 4 proteins (19-25 kDa) was specifically phosphorylated. This effect was completely mimicked by the Ca2+ ionophore A23187, whereas only two of these proteins (19 kDa and 25 kDa) were phosphorylated after cell exposure to the phorbol ester 12-O-tetradecanoylphorbol 13-acetate. By contrast, anti-Thy-1 mAb had no effect on the phosphorylation of these proteins, but induced specifically the phosphorylation of a protein of 32 kDa. These results therefore demonstrate that distinct activating pathways in T cells involve the phosphorylation of different proteins, suggesting that the stimulation of protein kinases in T lymphocytes is an early event in cell activation.

Interactions between the Thy-1 and T-cell antigen receptor pathways in the activation of cytotoxic T cells: evidence from synergistic effects, loss variants, and anti-CD8 antibody-mediated inhibition

The relationship between activation of cytolytic T-lymphocyte (CTL) clones via the T-cell receptor (Ti) or the Thy-1 molecule was investigated. Anti-Ti and anti-Thy-1 monoclonal antibodies (mAb) can activate CTL clones to secrete interferon-gamma (IFN-gamma). Suboptimal doses of anti-Ti and anti-Thy-1 mAb, as well as suboptimal doses of two different anti-Thy-1 mAb, can synergize to activate T-cell clones. The addition of phorbol myristic acetate (PMA), which is not stimulatory by itself, can enhance the synergistic effect of mAb on IFN-gamma production. Although the Ti and Thy-1 molecules were not found associated at the cell surface, the results presented here indicate that these molecules are functionally associated. Use of Ti loss variants of a CTL clone confirms that Thy-1-mediated signaling is not an alternative to, but is dependent on the Ti-mediated activation pathway. Additionally, use of anti-Lyt-2/3 mAb, previously described as interfering with class I MHC-Ti binding and/or activation and, in some cases, with anti-Ti-mediated activation revealed that anti-Thy-1 mAb-mediated activation was also greatly reduced by the presence of Lyt-2/3-specific mAb. Thus the interaction between Thy-1 and Ti might also involve Lyt-2 (Lyt-3) molecules.

A Thy-1.1-specific monoclonal alloantibody activates both mouse and rat T cells

In an attempt to further evaluate the role of Thy-1 in the antigen-independent triggering of mouse T cells, we have examined the activating properties of two Thy-1.1-specific mouse monoclonal antibodies (mAb). These reagents were established from an (A.TH X A.TL)F1 hybrid mouse (Thy-1b) immunized with IL-2 producing (BALB/c (Thy-1b) X BW5147 (Thy-1a)) T hybridoma cells. Although both mAb recognized the same Thy-1.1 determinant, one mAb of the gamma 3,kappa class (H171-146) was found to induce several T hybridoma cells to produce IL-2, and AKR thymocytes or cloned helper T cells to proliferate, whereas another mAb of the gamma 1,kappa class (H171-112) failed to do so even in the presence of phorbol myristic acetate (PMA). Increased IL-2 responses of T hybridoma cells were observed when the cell bound Thy-1.1-specific mAb were crosslinked by goat anti-mouse Ig (GaMIg) antibodies. Both a T-cell activating rat anti-Thy-1.2 mAb and the anti-Thy-1.1 mAb H171-146, although directed at distinct cell surface molecules, synergistically stimulated IL-2 production by T hybridoma cells. In addition, the mouse mAb H171-146 was found to stimulate LOU/M rat thymocytes to proliferate in the presence of exogenous IL-2. These data demonstrate that T cells can use Thy-1 as a signal-transducing molecule in both mouse and rat species, and support the notion that the activating properties of Thy-1.1-specific mAb are influenced by their heavy chain isotypes.

Thy-1: a lymphoid cell subset marker capable of delivering an activation signal to mouse T lymphocytes

Monoclonal anti-Thy-1 antibodies are capable of activating mouse T cells in the absence of an antigen-specific signal. Therefore, Thy-1 appears to be connected to an alternative signal transduction pathway, operative in thymocytes as well as in neuronal cells, since this molecule is also present on brain. Biochemical data have shown that this molecule is differentially glycosylated with respect to its cellular distribution. Structure and sequence comparisons revealed a strong homology with the immunoglobulin primordial domain. In addition, the Thy-1 glycoprotein has the particularity of being anchored to the membrane via a glycophospholipid tail. Gene transfer experiments in different cell types have been performed to analyze the mechanism of the Thy-1 pathway of activation.

Accessory molecules and T cell activation. II. Antibody binding to L3T4a inhibits Ia-independent mouse T cell proliferation

Monoclonal antibody (mAb) blocking assays using L3T4- and lymphocyte function-associated antigen-1 (LFA-1)-specific reagents were used as an approach to investigate the involvement of these accessory molecules in various T cell activation pathways. As previously reported, rat mAb to L3T4a and LFA-1A functional epitopes efficiently blocked antigen-driven T helper cell proliferation. In contrast, antigen- and Ia-independent T cell triggering induced by appropriate mAb to the Thy-1 or the T cell receptor molecules were found to be inhibitable by L3T4a- but not LFA-1A-specific mAb, although the extent of inhibition varied, depending on the cell type and the activating signal examined. These results provide further evidence that the inhibiting effects of L3T4-specific mAb on T cell responses may be due, in addition to an impairment of L3T4-class II major histocompatibility complex molecular interaction, to a down regulatory signal possibly transmitted by the L3T4 molecule itself.

Accessory molecules and T cell activation. I. Antigen receptor avidity differentially influences T cell sensitivity to inhibition by monoclonal antibodies to LFA-1 and L3T4

A series of BALB/c-derived T hybridoma cells, capable of producing interleukin 2 (IL 2) in response to poly(Glu60, Ala30, Tyr10) (GAT) presented by syngeneic B lymphoma cells in the context of Ad restriction determinants, was used as a model system to evaluate the roles of LFA-1 and L3T4 accessory molecules in antigen-specific T cell activation. Examination of the antigen requirement for optimal IL 2 responses revealed marked differences in the apparent avidity of these cells for GAT/Ad complexes. A relationship was observed between this parameter and the susceptibility of T hybridoma cells to inhibition by monoclonal antibodies directed at 5 distinct epitopes of LFA-1, and at A beta d allodeterminants. In contrast, L3T4a-specific monoclonal antibodies were found to block in a similar fashion the antigen-specific IL 2 responses of T hybridoma cells, regardless of the apparent avidity of their antigen receptors. It was also shown that both L3T4+ and L3T4- T hybridoma cells were capable of recognizing GAT plus Ad with high avidity. Thus, the quality of T cell antigen recognition appears to critically influence the involvement of LFA-1, and only to a marginal extent that of L3T4, in antigen-specific T cell activation. The implications of these findings are discussed in the context of recent data indicating that L3T4 may not only be an Ia-binding protein.

Identification of 5 topographic domains of the mouse LFA-1 molecule: subunit assignment and functional involvement in lymphoid cell interactions

We have evaluated the serologic and T cell function inhibiting properties of 10 rat mAb reactive with the mouse LFA-1 molecule. Binding inhibition studies revealed that these mAb identified five topographic domains on LFA-1, including an immunodominant epitope region (A) defined by 6 mAb (H35-89, H68-96, H85-326, H129-37, H154-595, and H155-141) and four other spatially separate epitopes each defined by a single mAb (i.e., B, H154-266; C, H129-296; D, H154-163; and E, H155-78). Immunoprecipitation studies carried out with T cell hybridoma detergent lysate containing native or dissociated alpha and beta LFA-1 subunits permitted assignment of the epitopes A, C, and D to the alpha-chain, while expression of the epitopes B and E required homologous pairing of the alpha and beta LFA-1 subunits. These anti-LFA-1 mAb did not bind to the Mac-1 positive P388D1 cells. All the six mAb directed at epitope A inhibited, in the range of 50 to 95%, the proliferative responses of alloantigen- or soluble-antigen GAT-specific T cell clones and the cytolytic activity of I-Ak-specific CTL clones. MAb reactive with the epitopes C and D also blocked these T cell responses, although to a lesser extent. No inhibition was observed with mAb specific to epitope B, whereas the epitope E-specific mAb H155-78 potentiated control T cell responses by 20 to 40%. Suboptimal amounts of anti-L3T4 mAb H129-19 were found to synergistically enhance the T cell function inhibiting properties of mAb to LFA-1 epitopes A, C, and D. These studies reveal an unexpected diversification of LFA-1 between mouse and rat species and further the functional dissection of this molecule.

Identification of 5 topographic domains of the mouse LFA-1 molecule: subunit assignment and functional involvement in lymphoid cell interactions

We have evaluated the serologic and T cell function inhibiting properties of 10 rat mAb reactive with the mouse LFA-1 molecule. Binding inhibition studies revealed that these mAb identified five topographic domains on LFA-1, including an immunodominant epitope region (A) defined by 6 mAb (H35-89, H68-96, H85-326, H129-37, H154-595, and H155-141) and four other spatially separate epitopes each defined by a single mAb (i.e., B, H154-266; C, H129-296; D, H154-163; and E, H155-78). Immunoprecipitation studies carried out with T cell hybridoma detergent lysate containing native or dissociated alpha and beta LFA-1 subunits permitted assignment of the epitopes A, C, and D to the alpha-chain, while expression of the epitopes B and E required homologous pairing of the alpha and beta LFA-1 subunits. These anti-LFA-1 mAb did not bind to the Mac-1 positive P388D1 cells. All the six mAb directed at epitope A inhibited, in the range of 50 to 95%, the proliferative responses of alloantigen- or soluble-antigen GAT-specific T cell clones and the cytolytic activity of I-Ak-specific CTL clones. MAb reactive with the epitopes C and D also blocked these T cell responses, although to a lesser extent. No inhibition was observed with mAb specific to epitope B, whereas the epitope E-specific mAb H155-78 potentiated control T cell responses by 20 to 40%. Suboptimal amounts of anti-L3T4 mAb H129-19 were found to synergistically enhance the T cell function inhibiting properties of mAb to LFA-1 epitopes A, C, and D. These studies reveal an unexpected diversification of LFA-1 between mouse and rat species and further the functional dissection of this molecule.

Analysis of the Thy-1 pathway of T cell hybridoma activation using 17 rat monoclonal antibodies reactive with distinct Thy-1 epitopes

Seventeen monoclonal anti-Thy-1 antibodies (mAb) derived from LOU/M rats immunized with mouse T cell clones were used to study the role of Thy-1 in antigen-independent T cell activation. These mAb identified Thy-1.2 or monomorphic determinants and immunoprecipitated a molecule of 25-28 kDa from detergent-solubilized, 125I-labeled T cell surface proteins. Competitive cross-inhibition binding assays demonstrated that these reagents defined 3 epitope groups including either Thy-1.2 (group A) or Thy-1 monomorphic (groups B and C) determinants. Experiments using high titered culture supernatants revealed that all 6 IgG mAb defining the epitope group C, and one IgG2c mAb directed at a determinant in group A were capable of stimulating the terpolymer-L-glutamic acid60-L-alanine33-Ltyrosine10 (GAT) plus I-Ad-reactive BALB/c T cell hybridoma T14-117.9 to produce interleukin 2 (IL2) in the absence of accessory cells. Cross-linking of cell-bound rat mAb by a BALB/c anti-rat kappa chain mAb, or the presence of B cell lymphomas in the culture resulted in an increase of the Thy-1-mediated IL2 responses of this hybridoma. Some mAb from group B required antibody doses exceeding 80 micrograms/ml in order to activate T cells, while others remained nonstimulatory at any dose tested. Striking synergy in mAb-mediated T cell activation was observed when nonmitogenic doses of mAb group groups A and C were mixed in the same culture. Analysis of a panel of GAT plus I-Ad-specific T cell hybridomas revealed that these cells markedly differed in the magnitude of their IL2 responses induced by a given amount of stimulating anti-Thy-1 mAb. Such reagents also stimulated normal thymocytes to express IL2 receptor on their surface. These studies show that the epitopic specificity and the amount of anti-Thy-1 mAb, and the susceptibility of the T cell examined represent important parameters for the triggering of the Thy-1 pathway of T cell activation.

L3T4 but not LFA-1 participates in antigen presentation by Ak-positive L-cell transformants

We report that mouse L cells expressing Ak class II molecules on their surface after DNA-mediated gene transfer are capable of presenting the synthetic copolymer (Glu60 Ala30 Tyr10) to Ak-restricted long-term T-cell clones. Antigen-induced T-cell stimulation could be inhibited by monoclonal antibodies (mAb) directed at spatially distinct determinants of the alpha and/or beta subunits of the Ak molecule, and by the rat L3T4-specific mAb H129.19. In contrast, several rat mAb reactive with the mouse LFA-1 molecule failed to inhibit T-cell activation when L cells were used as antigen-presenting cells (APC), although these mAb strongly inhibited the same T-cell responses in the presence of leukocytic APC. Similarly, the cytolytic activity of the Ak-specific T-cell clone A15.1.17 was blocked by L3T4-specific and by LFA-1-specific mAb when tested on Ak-positive B-cell hybridomas, but only by L3T4-specific mAb and not by LFA-1-specific mAb when Ak-positive L-cell transformants were used as targets. These data support the notion that the LFA-1 molecule is not necessary for T-cell activation, and suggest that its functional role as an accessory molecule depends on the leukocytic nature of the APC tested.

Clonospecific structural heterogeneity in the Thy-1 molecule from mouse T lymphocytes

The Thy-1 molecule immunoprecipitated from detergent-solubilized, 125I-labeled cell-surface proteins was shown to be processed in two distinct ways by mouse T lymphocytes: one leading to the expression by thymocytes, concanavalin A-activated spleen blasts, and six of nine T-cell clones of a molecule of 25-28 kd, and another, observed in three other T-cell clones, leading to the expression at their surface of a so far undescribed low Mr (23 kd) form of Thy-1. The results of two-dimensional gel electrophoresis and neuraminidase, endoglycosidase H, and endoglycosidase F treatment revealed that the observed heterogeneity of Thy-1 molecules from peripheral cloned T cells was due to major differences in the maturation and sialylation of their N-linked complex-type oligosaccharide residues. It was also found that a given T-cell clone could express T200, LFA.1, and transferrin receptor molecules with a low or high Mr. Furthermore, and in contrast to previously reported results, this study revealed that the differences in cell-surface glycoprotein profiles could not be correlated with the Lyt-2,3/T4 phenotypes, the specificity for allo-H-2, allo-I-A, allo-I-E, or GAT + I-Ak determinants, nor with the cytolytic or helper/amplifier potential of the various T-cell clones examined. The possible implications of these findings are discussed.