Immune response genes modulate serologic responses to Vibrio cholerae TcpA pilin peptides

Cholera is an enteric disease caused by Vibrio cholerae. Toxin-coregulated pilus (TCP), a type 4 pilus expressed by V. cholerae, is a cholera virulence factor that is required for host colonization. The TCP polymer is composed of subunits of TcpA pilin. Antibodies directed against TcpA are protective in animal models of cholera. While natural or recombinant forms of TcpA are difficult to purify to homogeneity, it is anticipated that synthesized TcpA peptides might serve as immunogens in a subunit vaccine. We wanted to assess the potential for effects of the immune response (Ir) gene that could complicate a peptide-based vaccine. Using a panel of mice congenic at the H-2 locus we tested the immunogenicity of TcpA peptide sequences (peptides 4 to 6) found in the carboxyl termini of both the classical (Cl) and El Tor (ET) biotypes of TCP. Cl peptides have been shown to be immunogenic in CD-1 mice. Our data clearly establish that there are effects of the Ir gene associated with both biotypes of TcpA. These effects are dynamic and dependent on the biotype of TcpA and the haplotypes of the host. In addition to the effects of the classic class II Ir gene, class I (D, L) or nonclassical class I (Qa-2) may also affect immune responses to TcpA peptides. To overcome the effects of the class II Ir gene, multiple TcpA peptides similar to peptides 4, 5, and 6 could be used in a subunit vaccine formulation. Identification of the most protective B-cell epitopes of TcpA within a particular peptide and conjugation to a universal carrier may be the most effective method to eliminate the effects of the class II and class I Ir genes.

Anti-class II monoclonal antibody-targeted Vibrio cholerae TcpA pilin: modulation of serologic response, epitope specificity, and isotype

Toxin-coregulated pilus (TCP) is a colonization factor required for cholera infection. It is not a strong immunogen when delivered in the context of whole cells, yet pilus subunits or TcpA derivative synthetic peptides induce protective responses. We examined the efficacy of immunizing mice with TCP conjugated to anti-class II monoclonal antibodies (MAb) with or without the addition of cholera toxin (CT) or anti-CD40 MAb to determine if the serologic response to TcpA could be manipulated. Anti-class II MAb-targeted TCP influenced the anti-TCP peptide serologic response with respect to titer and isotype. Responses to TcpA peptide 4 were induced with class II MAb-targeted TCP and not with nontargeted TCP. Class II MAb-targeting TcpA reduced the response to peptide 6 compared to the nontargeted TCP response. Class II MAb-targeted TcpA, if delivered with CT, enhanced the serologic response to TcpA peptides. The effectiveness of the combination of targeted TCP and CT was reduced if anti-CD40 MAb were included in the primary immunization. These data establish the need to understand the role of TCP presentation in the generation of B-cell epitopes in order to optimize TcpA-based cholera vaccines.

Evaluation of cholera vaccines formulated with toxin-coregulated pilin peptide plus polymer adjuvant in mice

Cholera is an acute diarrheal disease that is caused by the gram-negative bacterium Vibrio cholerae. The low efficacy of currently available killed-whole-cell vaccines and the reactinogenicity coupled with potential reversion of live vaccines have thus far precluded widespread vaccination for the control of cholera. Recent studies on the molecular nature of the virulence components that contribute to V. cholerae pathogenesis have provided insights into possible approaches for the development of a defined subunit cholera vaccine. Genetic analysis has demonstrated that the toxin-coregulated pilus (TCP) is the major factor that contributes to colonization of the human intestine by V. cholerae. In addition, polyclonal and several monoclonal antibodies directed against TCP have been shown to provide passive immunity to disease in the infant mouse cholera model. In the present study, synthetic peptides corresponding to portions of the C-terminal disulfide region of TcpA pilin were formulated with polymer adjuvants currently in clinical trials and used to actively immunize adult female CD-1 mice. The experimental vaccine formulations elicited high levels of antigen-specific immunoglobulin G (IgG), including a broad spectrum of subclasses (IgG1, IgG2a, IgG2b, and IgG3), and lower levels of IgA. Infant mice born to the immunized mothers showed 100% protection against a 50% lethal dose (1 LD(50)) challenge and 50% protection against a 10-LD(50) challenge with virulent strain O395. These results indicate that specific regions of TcpA, including those delineated by the peptides used in this study, have the potential to be incorporated into an effective defined subunit vaccine for cholera.

Molecular dynamics of point mutated I-A(k) molecules expressed on lymphocytes

We have recently reported the lateral and rotational diffusion parameters for I-A(k) molecules expressing various cytoplasmic truncations (Int. Immunol. 12 (2000) 1319). We now describe the membrane dynamics of I-A(k) with various mutations in the presumed contact region between alphabeta-heterodimers in an (alphabeta)2 dimer of dimers structure. Such mutations are known to strongly affect the antigen presentation ability of these molecules (Int. Immunol. 10 (1998) 1237-1249) but cause relatively small changes in the molecular dynamics of I-A(k). Lateral diffusion coefficients of I-A(k) wild-type molecules and mutants obtained via fringe fluorescence photobleaching recovery (FPR) ranged from 1.1 to 2.3x10(-10)cm2/s at room temperature while fractional mobilities averaged 75+/-6%. For all cell types examined, treatment with either hen egg lysozyme 46-61 peptide or db-cAMP reduced the I-A(k) mobile fraction by about 10% relative to untreated cells, suggesting that these treatments may increase lateral confinement of class II in lipid rafts or cytoskeletal interactions of the molecules. Wild-type I-A(k) and mutants capable of normal or partial antigen presentation exhibited, as a group, slightly longer rotational correlation times (RCT) at 4 degrees C than did mutants inactive in antigen presentation, 14+/-4 versus 10+/-1 micros, respectively. Moreover, peptide, cAMP and anti-CD40 mAb treatment all increased rotational correlation times for fully- and partially-functional I-A(k) but not for non-functional molecules. For example, 16 h peptide treatment yielded average RCTs of 28+/-12 and 10+/-1 micros for the groups of functional and non-functional molecules, respectively. Such modulation of the dynamics of functional class II molecules is consistent with these treatments' stabilization of class II or induction of new gene expression. Measurements of fluorescence resonant energy transfer between I-A(k), though complicated by cellular autofluorescence, averaged 6+/-7% over 15 cells or treatments, a result consistent with the presence of a small fraction of I-A(k) as a dimer of dimers species. In summary, our results suggest subtle changes in the molecular motions of class II molecules correlate with a significant impact on class II function. Molecules active in antigen presentation exhibit more restricted motion in the membrane, and thus presumably more extensive intermolecular interactions, than non-functional molecules. Further, treatments, such as db-cAMP and anti-CD40, which rescue antigen presentation by partially defective mutants, appear to increase such interactions, several types of which have already been reported for class II. A more detailed understanding of these phenomena will require both more sensitive biophysical tools and a more refined model of the role of class II intermolecular interactions in antigen presentation.

Fc alpha receptor cross-linking causes translocation of phosphatidylinositol-dependent protein kinase 1 and protein kinase B alpha to MHC class II peptide-loading-like compartments

A20 IIA1.6 B cells cotransfected with FcalphaR and wild-type gamma-chain (wt-ITAM (immunoreceptor tyrosine-based activation motif)) or FcalphaR and gamma-chain, in which the wt-ITAM was substituted with the FcgammaRIIA ITAM (IIA-ITAM), were used to investigate cell signaling events influencing presentation of FcalphaR-targeted exogenous Ag in the context of MHC class II. wt-ITAM cells presented FcalphaR-targeted OVA more efficiently than IIA-ITAM transfectants to OVA-specific T cell hybridomas. Phosphatidylinositol 3-kinase (PI 3-kinase) inhibition abrogated Ag presentation, suggesting that FcalphaR may trigger a PI 3-kinase-dependent signal transduction pathway, and thus phosphatidylinositol-dependent protein kinase (PDK1) and protein kinase B alpha (PKBalpha) activation. Cross-linking FcalphaR on wt-ITAM or IIA-ITAM cells triggered equivalent PI 3-kinase-dependent activation of PKBalpha. Furthermore, FcalphaR cross-linking triggered recruitment of PDK1 and serine-phosphorylated PKBalpha to capped cell surface FcalphaR irrespective of the gamma-chain ITAM. Although FcalphaR endocytosis was accompanied by translocation of PDK1 and phospho-PKBalpha to FcalphaR-containing vesicles in both transfectants, this was decreased in IIA-ITAM cells, and a significant proportion of PDK1 and PKBalpha remained at the plasma membrane. In wt-ITAM cells, PDK1 and serine-phosphorylated PKBalpha translocated to lysosomal-associated membrane glycoprotein 1- and cathepsin B-containing vesicles, consistent with MHC class II peptide-loading compartments (MIIC) described by other groups. Our data indicate that translocation of signal transduction mediators to MIIC-like compartments accompanies efficient presentation of receptor-targeted Ag, and suggest a mechanism connecting signaling to the Ag-processing pathway.

Dendritic cell longevity and T cell persistence is controlled by CD154-CD40 interactions

Inflammatory mediators facilitate the maturation of dendritic cells (DC), enabling them to induce the activation, proliferation and differentiation of cognate T cells. The role of CD40 on DC and CD154 on T cells has been studied by the co-adoptive transfer of antigen-pulsed DC and TCR-transgenic (Tg) T cells in vivo. It is shown that in the absence of CD40-CD154 interactions, initial Tg T cell expansion occurs in vivo, but over time, T cell expansion cannot be sustained. The basis for the demise of the T cell population is likely due to the disappearance of the antigen-pulsed DC in the draining lymph nodes when CD154-CD40 interactions are interrupted. These findings show that both T cell and DC persistence in vivo is dependent on CD40-CD154 interactions. In addition to the physical persistence of the DC, CD40 triggering of DC also greatly increases the period for which they can productively present antigen to Tg T cells. Hence DC persistence and antigen-presenting cell capacity are both dependent on CD40 signaling. While TNF-alpha can mature DC as measured by a variety of criteria, the unique capacity of CD40 signaling to sustain T cell responses and induce DC maturation is underscored by the inability of TNF-alpha to rescue the immune deficiency of CD40(-/-) DC. Hence, the profound impact of CD154 deficiency on cell-mediated immunity may be due to its ability to limit the duration of antigen presentation in vivo and cause the premature demise of antigen-specific T cells.

Dendritic cell longevity and T cell persistence is controlled by CD154-CD40 interactions

Inflammatory mediators facilitate the maturation of dendritic cells (DC), enabling them to induce the activation, proliferation and differentiation of cognate T cells. The role of CD40 on DC and CD154 on T cells has been studied by the co-adoptive transfer of antigen-pulsed DC and TCR-transgenic (Tg) T cells in vivo. It is shown that in the absence of CD40-CD154 interactions, initial Tg T cell expansion occurs in vivo, but over time, T cell expansion cannot be sustained. The basis for the demise of the T cell population is likely due to the disappearance of the antigen-pulsed DC in the draining lymph nodes when CD154-CD40 interactions are interrupted. These findings show that both T cell and DC persistence in vivo is dependent on CD40-CD154 interactions. In addition to the physical persistence of the DC, CD40 triggering of DC also greatly increases the period for which they can productively present antigen to Tg T cells. Hence DC persistence and antigen-presenting cell capacity are both dependent on CD40 signaling. While TNF-alpha can mature DC as measured by a variety of criteria, the unique capacity of CD40 signaling to sustain T cell responses and induce DC maturation is underscored by the inability of TNF-alpha to rescue the immune deficiency of CD40(-/-) DC. Hence, the profound impact of CD154 deficiency on cell-mediated immunity may be due to its ability to limit the duration of antigen presentation in vivo and cause the premature demise of antigen-specific T cells.

Class II-targeted antigen is superior to CD40-targeted antigen at stimulating humoral responses in vivo

We examined the efficacy of using monoclonal antibodies to target antigen (avidin) to different surface molecules expressed on antigen presenting cells (APC). In particular, we targeted CD40 to test whether the "adjuvant" properties of CD40 signaling combined with targeted antigen would result in enhanced serologic responses. We targeted avidin to class II as a positive control and to CD11c as a negative control. These surface proteins represent an ensemble of surface molecules that signal upon ligation and that are expressed on professional APC, in particular dendritic cells (DC). We observed that targeting class II molecules on APC was superior to targeting CD40, or CD11c. However, CD40 and CD11c could function as targets for antigen bound monoclonal antibodies under certain conditions. Interestingly, inclusion of anti-CD40 mAb with the targeting anti-class II-targeted antigens negatively affects humoral response, suggesting that CD40 signaling under certain conditions may suppress processing and/or presentation of targeted antigen.

Presentation of ovalbumin internalized via the immunoglobulin-A Fc receptor is enhanced through Fc receptor gamma-chain signaling

The mechanism of enhanced presentation of ovalbumin (OVA) internalized as immunoglobulin A (IgA)-OVA via the IgA Fc receptor (FcalphaR) was analyzed by focusing on the role of the FcalphaR-associated gamma chain. Comparison of B-cell transfectants expressing FcalphaR plus wild-type (WT) gamma chain or gamma chain in which the immunoreceptor tyrosine-based activation motif (ITAM) was altered by tyrosine mutation or substitution with the ITAM of FcgammaRIIA showed that signaling-competent ITAM was not required for endocytosis of IgA-OVA. However, antigen presentation was impaired by ITAM changes. Signaling-competent gamma-chain ITAM appeared necessary for transport of ligated FcalphaR to a lamp-1(+) late endocytic compartment for remodeling and/or activation of that compartment and also for efficient degradation of IgA complexes. Moreover, FcalphaR ligation also activated efficient processing of nonreceptor-targeted antigen. The results suggest that gamma-chain signaling activates the antigen processing compartment.

The ins and outs of getting in: structures and signals that enhance BCR or Fc receptor-mediated antigen presentation

Antigen-presenting cells internalize antigen by fluid-phase pinocytosis or by endocytosis via surface receptors such as the B cell receptor (BCR) and Fc receptors for IgG, IgA and IgE (FcR). While both modes of internalization lead to antigen presentation it is recognized that receptor-mediated endocytosis greatly enhances the efficiency of processing and antigen presentation. Receptors facilitate the entry of antigen into the endocytic pathway by interaction of their internalization motifs with the endocytic machinery. These motifs include tyrosine-based, dileucine and casein kinase-like motifs. However these structures appear insufficient to support processing of cryptic epitopes, leading to a limited immune response. Cryptic epitope processing appears dependent on receptor signaling which is mediated by immunoreceptor tyrosine activation motifs (ITAMs). The signaling cascade which follows receptor crosslinking promotes reorganization and acidification of the late endocytic compartment or MIIC. Signaling events downstream of Syk, in particular calcium flux and protein kinase C activation, are necessary for MIIC induction. PI(3) kinase is also involved at multiple steps in antigen presentation, including production of PIP3 and transport of cathepsins. PIP3 is crucial both as a binding substrate for proteins implicated in vesicle transport and for the recruitment of signaling molecules to the plasma membrane. Among PIP3 activated molecules, protein kinase B (PKB) has been linked to endocytic function. We observe association of activated PKB with the MIIC after signaling through antigen presentation-competent receptors, but not mutant, presentation-defective receptors.

Rotational and lateral dynamics of I-A(k) molecules expressing cytoplasmic truncations

Rotational and lateral diffusion of I-A(k) molecules with various alpha and beta chain cytoplasmic truncations known to affect class II function were measured to assess the role of cytoplasmic domains in regulating I-A(k) molecular motions. Deletion of all 12 alpha chain C-terminal residues and all 18 corresponding beta chain residues (alpha-12/beta-18) is known to abrogate translocation of protein kinase C to the nucleus upon class II cross-linking. Similarly, truncation of the entire cytoplasmic alpha chain domain and the 10 C-terminal residues of the beta chain impairs presentation of antigenic peptides to T cells. The rotational correlation time of the wild-type molecule, 11.9 +/- 2.6 micros as measured by time-resolved phosphorescence anisotropy, decreased to 7. 2 +/- 3.7 micros in the fully truncated alpha-12/beta-18 protein. Other truncated class II molecules exhibited only small changes in molecular rotation rates relative to the wild-type. The rate of lateral diffusion of the fully truncated molecule, measured with two independent methods, 2.3 x 10(-10) cm(2)/s, was comparable with that of the wild-type molecule. Thus, it appears that the alpha and beta chain cytoplasmic domains regulate the molecular motions of unperturbed I-A(k) molecules only modestly, despite the known involvement of these regions in class II signaling. Various explanations for this behavior are discussed, e.g. the possibility that class II membrane complexes are sufficiently large that association and dissociation of specific signaling proteins during antigen presentation do not significantly perturb the apparent molecular motions of the complex.

Mutations in specific I-A(k) alpha(2) and beta(2) domain residues affect surface expression

A previous investigation demonstrated that several mutations in class II dimer-of-dimers contact residues interfere with antigen presentation by transfectants but not with plasma membrane expression of the mutant class II. In the present study we examined other class II mutations in this region that did inhibit plasma membrane expression of mutant class II molecules. Molecules containing both mutations H alpha 181D in the alpha(2) domain and E beta 170K in the beta(2) domain exhibited low plasma membrane expression, but molecules with only one of these mutations were expressed normally. The mutant class II molecules were transported to organelles that were accessible to a fluid-phase protein, hen egg lysozyme (HEL). Culture of transfectants with lysozyme enhanced the amount of class II compact dimer (alpha beta plus peptide; CD), and this was especially marked for the class II mutant H alpha 181D/E beta 170K and for other molecules possessing both mutations. Formation of class II CD was not paralleled by an increase in class II surface expression. Thus the joint mutation of H alpha 181 and E beta 170 has two effects. In the absence o high concentrations of exogenous peptide, it prevents efficient CD formation, possibly by affecting invariant chain (Ii) proteolysis and/or the stability of the class II after Ii/CLIP is removed. At high peptide concentrations supplied by exogenous HEL, the mutations allow CD formation, but not expression of class II on the plasma membrane. Molecular modeling of the possible interaction of class II and Ii suggests that the mutant amino acids H alpha 181D and E beta 170K, besides affecting the overall stability of class II, might also interact with Ii via two loops in class II's alpha(2) and beta(2) domains respectively.

Gamma-chain dependent recruitment of tyrosine kinases to membrane rafts by the human IgA receptor Fc alpha R

We show that the human IgA receptor, Fc alpha R, redistributes to plasma membrane rafts after cross-linking and that tyrosine kinases are relocated to these sites following Fc alpha R capping. We demonstrate by confocal microscopy that Fc alpha R caps in membrane rafts by a gamma-chain-independent mechanism but that gamma-chain expression is necessary for Lyn redistribution. Immunoblotting of rafts isolated by sucrose density gradient centrifugation demonstrated recruitment of gamma-chain and phosphorylated tyrosine kinases Lyn and Bruton's tyrosine kinase to membrane rafts after Fc alpha R cross-linking. Time-dependent differences in Lyn phosphorylation and Bruton's tyrosine kinase distribution were observed between cells expressing Fc alpha R plus gamma-chain and cells expressing Fc alpha R only. This study defines early Fc alpha R-triggered membrane dynamics that take place before Fc alpha R internalization.

Dynamics of molecules involved in antigen presentation: effects of fixation

Antigen presentation by MHC class II molecules can be enhanced by paraformaldehyde fixation of antigen-presenting cells prior to assay. This treatment might be expected to aggregate membrane proteins and thus stabilize and strengthen transient protein-protein interactions involved in intercellular cooperation. Lateral and rotational dynamics of the MHC class II antigen I-Ad on A20 cells fixed with various concentrations of paraformaldehyde were examined by fluorescence photobleaching recovery and time-resolved phosphorescence anisotropy, respectively. Probes were tetramethylrhodamine and erythrosin conjugates of MKD6 Fab fragments. Increasing concentrations of paraformaldehyde led to a progressive increase in the limiting anisotropy of I-Ad at 4 degrees C from the value of 0.042 for untreated cells, indicative of large aggregate formation, while leaving the rotational correlation time of 29 micros unchanged, a measure of the unperturbed molecule. On the other hand, the translational diffusion constants decreased from approximately 2x10(-10) cm2 s(-1), while the fractional recovery remained unchanged at about 40-50%. Taken together, these results suggest that fixation crosslinks class II molecules to each other or to other membrane proteins into structures large enough (>500,000 kDa) to diffuse translationally with perceptibly size-dependent rates. The fixation effects on both class II rotation and lateral diffusion were half-maximal at paraformaldehyde concentrations of approximately 0.2%. Possible relations between the biological effector functions of class II and the physical sizes of fixation-induced aggregates are discussed.

Dichotomy between naïve and memory CD4(+) T cell responses to Fas engagement

Engagement of Fas (APO-1, CD95), a member of the tumor necrosis factor receptor superfamily, can induce apoptotic cell death. However, Fas engagement also can costimulate lymphocyte proliferation. The physiologic regulation of these two outcomes is poorly understood. Here, we have used two systems, the first in vitro and the second in vivo, to demonstrate that naïve and memory CD4(+) T cells display dichotomous responses to Fas ligation. Naïve CD4(+) T cells (CD44(lo), CD45RB+, CD62L+) die as a consequence of Fas ligation in the presence of anti-CD3 antibody, whereas memory T cells (CD44(hi), CD45RB-, CD62L-), freshly isolated from the same starting population and subjected to the same stimulation conditions, are costimulated to proliferate by Fas ligation. In vitro, we demonstrate that CD28-mediated signals or T helper 1 and T helper 2 differentiation cytokines alter the response of naïve T cells, but not of memory T cells, to Fas ligation. In vivo experiments in hen egg lysozyme (HEL) T cell receptor transgenic mice show that CD4(+) T cells from HEL-naïve mice are killed by Fas ligation, but CD4(+) T cells from long-term HEL-exposed mice are costimulated by Fas ligation. Thus, the physiological outcome of Fas ligation in CD4(+) T cells is determined primarily by the antigenic history of the T cell.

Salt bridge residues between I-Ak dimer of dimers alpha-chains modulate antigen presentation

Class II dimers of dimers are predicted to have functional significance in antigen presentation. The putative contact amino acids of the I-Ak class II dimer of dimers have been identified by molecular modeling based on the DR1 crystal structure (Nydam et al., Int. Immunol. 10, 1237,1998). We have previously reported the role in antigen presentation of dimer of dimers contact amino acids located in the C-terminal domains of the alpha- and beta-chains of class II. Our calculations show that residues Ealpha89 and Ralpha145 in the alpha2-domain form an inter alpha-chain salt bridge between pairs of alphabeta-heterodimers. Other residues, Qalpha92 and Nalpha115, may be involved in close association in that part of the alpha-chain. We investigated the role of these amino acids on class II expression and antigen presentation. Class II composed of an Ealpha89K substituted alpha-chain paired with a wt beta-chain exhibited inhibited antigen presentation and expression of alpha-chain serologic epitopes. In contrast, mutation of Ralpha145E had less affect on antigen presentation and did not affect I-Ak serologic epitopes. Interchanging charges of the salt bridge residues by expressing both Ralpha145E and Ealpha89K on the same chain obviated the large negative effect of the Ealpha89K mutation on antigen presentation but not on the serologic epitopes. Our results are similar for those reported for mutation of DR3's inter-chain salt bridge with the exception that double mutants did not moderate the DR3 defect. Interestingly, the amino acids differences between I-A and DR change the location of the inter-chain salt bridges. In DR1 these residues are located at positions Ealpha88 and Kalpha111; in I-Ak these residues are located at position Ealpha89 and Ralpha145. Inter alpha-chain salt bridges are thus maintained in various class II molecules by amino acids located in different parts of the alpha2-domain. This conservation of structure suggests that considerable functional importance may attach to the ionic interactions.

Mutations in MHC class II dimer of dimers contact residues: effects on antigen presentation

The recent solutions of the MHC class II crystal structure reveal dimerization of the alphabeta heterodimers. These dimer of dimers structures may also exist either on resting cells or after engagement by TCR, and may be involved in B cell signaling and up-regulation of co-stimulatory molecules such as B7 which facilitate T cell activation. By combining crystallographic data on HLA-DR1 with the sequence of murine I-Ak and refining the resulting structure through energy minimization calculations, we have predicted the contact amino acids expected to stabilize the I-Ak dimer of dimers structure. As in HLA-DR1, three salt bridges in I-Ak (D alpha62-Hbeta112, H alpha181-E beta163, E alpha183-Hbeta113) appear to provide the main interaction. Guided by this structural data, we prepared 45 B cell transfectants representing 20 different class II mutation phenotypes in the contact region containing these salt bridges. We examined their abilities to activate three T cell hybrids. Antigen-specific h4Ly50.5 cells were not greatly affected by changes in the dimer of dimer contact residues. In contrast, autoreactive C8.A3 T cells were very sensitive to changes in this region but presentation of class II of many mutation phenotypes could be rescued by treatments that up-regulate B7-1. The alloreactive hybridoma 2H40.2.5 was less sensitive to changes in the contact residues. A simple model was developed that summarizes the effects of the mutations for the T cells tested. Mutations at D alpha162, E alpha183, H alpha181 and Rbeta106 had the largest negative impact, while D alpha166, E alpha185, Hbeta112, Hbeta113 and E beta163 were less disruptive. Results are consistent with mutations interfering with class II interaction with another molecule which might or might not be another class II heterodimer. However, the larger negative impact of alpha chain mutations in salt bridge pairs suggests that these sites also help maintain some essential conformation of the alpha chain apart from any possible impact on dimer of dimers stability.

Interferometric fringe fluorescence photobleaching recovery interrogates entire cell surfaces

Fluorescence photobleaching recovery (FPR) measurements of cell surface protein lateral diffusion typically employ an interrogated spot of 0.5 microm 1/e2 radius. The effective spot area represents only 1/500 of the total surface of an 8-microm cell. An FPR measurement of a protein expressed as 50,000 copies per cell reflects the dynamics of 100 molecules. This limits the precision and reproducibility of FPR measurements. We describe a method for interferometric fringe pattern FPR that permits simultaneous interrogation of the entire cell's surface. Fringe patterns are generated interferometrically within the optical path of an FPR system. Methods for interpreting fluorescence recovery kinetics on cells and for determining the protein mobile fraction are presented. With fringe FPR, the murine major histocompatibility complex class II antigen I-Ak expressed on M12.C3.F6 cells has 100-fold improved fluorescence signals relative to spot FPR, with corresponding improvements in signal-to-noise ratios of recovery traces. Diffusion coefficients (+/- standard deviation) of (2.1 +/- 0.4) x 10(-10) and (1.8 +/- 1.0) x 10(-10) cm2 s-1 with corresponding mobile fractions of I-Ak of 66.1 +/- 7.8% and 63.4 +/- 18.0% were obtained by fringe and spot methods, respectively. The improved reproducibility of fringe over spot results is less than signal improvements predict. There may thus be substantial variation from cell to cell in protein dynamics, and this method may permit the assessment of such variation.

Increased inhibition of proliferation of human B cell lymphomas following ligation of CD40, and either CD19, CD20, CD95 or surface immunoglobulin

Non-Hodgkin's (NHL) B cell lymphomas are growth-inhibited by ligation of their CD40 molecules. This inhibition is not absolute in that approximately 50% of the cells are not inhibited. We conducted studies to see if other signals that have been reported to inhibit B cell lymphoma growth could be used in combination with anti-CD40 signaling to completely inhibit growth. Ligation of surface immunoglobulin (Ig), CD19, CD20, CD37 or CD95 with soluble antibody did not affect growth of the panel of NHL cells examined. Ligation of CD20, CD19 or CD95 was inhibitory for some NHL cell lines if the primary antibody was crosslinked with a secondary antibody. Combining anti-CD40 with anti-CD19, anti-CD20, or anti-Ig resulted in increased inhibition past that produced by anti-CD40 alone. The additive effect of anti-CD40 and other antibodies to selected surface markers was not observed in all NHL cell lines. Crosslinking of CD95 was also growth inhibitory for the majority of the NHL, and when combined with anti-CD40 under conditions that afforded crosslinking of the two receptors, increased inhibition was seen in three of the NHL cell lines. We found that cAMP or sodium butyrate (NaB) were also effective at inhibiting growth of the NHL cells; this was a profound inhibition (approaching 100%) compared to the 50% inhibition seen with anti-CD40 treatment. The potential for anti-CD40 and either cAMP or NaB to be additive was tested and not found to be the case. The ability to inhibit proliferation of the NHL was very dynamic with some antibody combinations being either inhibitory for multiple cells, not having an effect at all, or in some cases being stimulatory. This suggests that the NHL may represent unique stages of B cells that might serve as a model system which could be developed to precisely categorize patient NHL.

Lateral dynamics of major histocompatibility complex class II molecules bound with agonist peptide or altered peptide ligands

We examined the lateral diffusion of I-Ad on A20 cells following the binding of ovalbumin-derived peptides. The peptides were OVA323-339 and OVA325-335 and a related peptide OVA325-335s substituted H331Q. Only OVA323-339 and OVA325-335 were effectively presented by A20 cells to DO-11.10/S4.4 T cells as assessed by IL-2 production. Fluorescence photobleaching recovery (FPR) measurements showed anti-I-Ad to have a lateral diffusion coefficient on untreated A20 cells of 1.8 +/- 1.0 x 10(-10) cm2 s-1 at 25 degrees C with fluorescence recovery after photobleaching greater than 50%. After 24 h incubation of A20 cells with OVA323-339 or OVA325-335, a subpopulation of A20 cells appeared that were approximately half the size of untreated A20 cells. Culture of A20 with OVA325-355s did not stimulate DO-11.10 cells or induce a size change in A20 cells. Class II molecules were laterally immobile on these small cells with fluorescence recoveries after photobleaching of less than 20%. The relative number of small cells in the A20 cell population was correlated with the immunogenicity of the peptides. These results suggest that immobilization of surface I-Ad may be an important event in antigen presentation.

Truncated MHC class II cytoplasmic and transmembrane domains: effect on plasma membrane expression

Plasma membrane (PM) expression of major histocompatibility complex (MHC) class II molecule is required for the interaction of antigen (Ag) presenting cells and T lymphocytes. Class II molecules composed of an alpha and a beta chain are highly polymorphic which facilitates their interaction with Ag and Ag-specific T cells. Recently, we have focused on the less polymorphic sequences of class II molecules, the transmembrane (TM) and cytoplasmic (Cy) domains, in an attempt to understand what their function might be. Using site-directed mutagenesis to create truncations in the TM and Cy domains of IAk's alpha or beta chain, or both, we have identified some of the sequence requirements for efficient surface expression of I-Ak molecules. Ak beta TM mutants that are not expressed at the PM are not transported past the medial-Golgi as indicated by in situ staining and Western blot analysis of endoglycosidase-H-treated immunoprecipitates. The lack of transport of TM class II mutants is not due to lack of association with the invariant chain (Ii). Class II molecules with Cy domain truncations in both chains are not efficiently transported to the PM and also have a percentage of molecules that are endoglycosidase-H sensitive. In situ staining of class II in cells expressing Cy domain truncated class II molecules revealed a discrete vesicular pattern compared to the staining of transfectants that expressed wildtype class II molecules. The immunofluorescence data along with the endoglycosidase-H data indicate the Cy domains are required for efficient transport. Immunoprecipitation studies using a panel of I-Ak conformation-specific antibodies revealed that the truncation of the Cy domains of both chains did not effect the conformation of class II. However, further truncation of the Ak beta chain into the TM domain resulted in lack of transport past the ER/medial-Golgi and diminished expression (stability) of mutant class II proteins within the cells. The alpha/beta chains of the TM mutants that did associate bound a panel of conformation sensitive antibodies except for one, 3F12. We conclude that the Cy domain of the alpha and beta chains of MHC class II, as well as sequences in the TM domains of the Ak beta chain are required for efficient class II PM expression. The reason for the lack of PM expression of TM mutants may be the inability to assess a transport competent conformation as defined by the 3F12-specific epitope, while truncation of the Ak alpha Cy domains is proposed to prevent complete masking of the ER retention sequence of the Ii chain.

Role of 4-1BB ligand in costimulation of T lymphocyte growth and its upregulation on M12 B lymphomas by cAMP

K46J B lymphomas express a T cell costimulatory activity that is not inhibited by CTLA-4Ig, anti-B7-1, anti-B7-2, anti-intercellular adhesion molecule 1 or antibodies to heat stable antigen. In this paper we report that this costimulatory activity is mediated at least in part by 4-1BB ligand, a member of the tumor necrosis factor (TNF) gene family that binds to 4-1BB, a T cell activation antigen with homology to the TNF/nerve growth factor receptor family. A fusion protein between 4-1BB and alkaline phosphatase (4-1BB-AP) blocks T cell activation by K46J lymphomas in both an antigen-specific system and with polyclonally (anti-CD3) activated T cells. 4-1BB-AP also blocks antigen presentation by normal spleen cells. When the antigen-presenting cells express B7 molecules as well as 4-1BB ligand, we find that B7 molecules and 4-1BB-AP both contribute to T cell activation. These data suggest that 4-1BB ligand plays an important role in costimulation of IL-2 production and proliferation by T cells. The B lymphoma M12 expresses low levels of 4-1BB-L but can be induced to express higher levels by treatment of the B cells with cAMP, which also induces B7-1 and B7-2 in these cells. Thus cAMP appears to coordinately induce several costimulatory molecules on B cells.

Class II cytoplasmic and transmembrane domains are not required for class II-mediated B cell spreading

B cells cultured on immobilized anti-class II monoclonal antibody (mAb) change from round to flattened cells, with lamellipodia and filopodia. This change in cell morphology, termed 'spiders', occurs within 30 min upon culture and is mediated through either I-A or I-E molecules. Class II molecules that are defective in mediating protein kinase C (PKC) due to the deletions of both alpha and beta chain's cytoplasmic (Cy) domain sequences can induce spider formation. B-cell transfectants that express chimeric MHC class II/class I molecules, where the ectodomains are class II sequences and the transmembrane and Cy domains are class I sequences also form spiders when cultured on anti-class II mAb. The spider morphology is not induced by either anti-immunoglobulin (Ig) or anti-MHC class I mAb. Treatment of B cells to increase intracellular cAMP, a component of the class II signaling pathway also results in spider formation with the same kinetics and percent change in the responding population as that induced by anti-class II mAb. Cytochalasin A treatment which disrupts cytoskeletal actin filaments and the tyrosine kinase inhibitor, genistein, both inhibit spider formation. Actin redistributes from a concentric ring in round cells to the ends of the filopodia in the spiders. The mechanism of spider induction whether resultant from second messengers following class II signaling or from non-signaling-induced physical interactions of class II with intracellular cytoskeletal components only requires the extracellular domains of class II. The biologic relevance of B-cell spiders is currently not known but has been reported to be associated with class II signal transduction and efficient Ag presentation.

MHC class II molecules that lack cytoplasmic domains are associated with the cytoskeleton

MHC class II molecules, composed of alpha- and beta-chain heterodimers, are required for Ag presentation. The carboxyl-terminal domains of class II molecules are believed to mediate the location of class II in the plasma membrane and are important for signal transduction and Ag presentation. These domains contain typical transmembrane sequences, and cytoplasmic sequences of 12 or 18 amino acids for the alpha- and beta-chains, respectively. We examined these domains to determine whether they linked class II molecules to the actin-based cytoskeleton. Our analyses of class II-cytoskeleton interactions, such as a colocalization with actin filaments during capping, association with the detergent-insoluble cytoskeleton, and direct binding of filamentous actin, revealed that both the cytoplasmic and transmembrane domains contributed to class II interactions with the cytoskeleton. Detergent-extracted and immunoprecipitated full-length class II molecules had quantitatively stronger interactions with the cytoskeleton than did molecules with deleted cytoplasmic domains. A secondary Ab, which was used to cross-link primary Ab bound to class II, up-regulated the class II-cytoskeletal associations. This association was efficiently inhibited by dihydrocytochalasin B, but only partially disrupted by chlorpromazine. The mechanism of interaction with actin filaments after ligation of class II occurred without a measurable increase in filamentous actin levels. This suggested that enhanced class II-cytoskeleton associations involved a rearrangement of existing actin filaments, possibly through the multiple kinases that are activated after class II transmembrane signaling.

MHC class II molecules that lack cytoplasmic domains are associated with the cytoskeleton

MHC class II molecules, composed of alpha- and beta-chain heterodimers, are required for Ag presentation. The carboxyl-terminal domains of class II molecules are believed to mediate the location of class II in the plasma membrane and are important for signal transduction and Ag presentation. These domains contain typical transmembrane sequences, and cytoplasmic sequences of 12 or 18 amino acids for the alpha- and beta-chains, respectively. We examined these domains to determine whether they linked class II molecules to the actin-based cytoskeleton. Our analyses of class II-cytoskeleton interactions, such as a colocalization with actin filaments during capping, association with the detergent-insoluble cytoskeleton, and direct binding of filamentous actin, revealed that both the cytoplasmic and transmembrane domains contributed to class II interactions with the cytoskeleton. Detergent-extracted and immunoprecipitated full-length class II molecules had quantitatively stronger interactions with the cytoskeleton than did molecules with deleted cytoplasmic domains. A secondary Ab, which was used to cross-link primary Ab bound to class II, up-regulated the class II-cytoskeletal associations. This association was efficiently inhibited by dihydrocytochalasin B, but only partially disrupted by chlorpromazine. The mechanism of interaction with actin filaments after ligation of class II occurred without a measurable increase in filamentous actin levels. This suggested that enhanced class II-cytoskeleton associations involved a rearrangement of existing actin filaments, possibly through the multiple kinases that are activated after class II transmembrane signaling.

Truncation of the A alpha chain of MHC class II molecules results in inefficient antigen presentation to antigen-specific T cells

Antigen presenting cells (APC) expressing MHC class II molecules composed of chains with part or all of the cytoplasmic domains deleted are inefficient at presenting hen egg lysozyme peptides to antigen specific T cell hybrids compared with APC that express wild-type MHC class II molecules. This effect is most apparent for mutants in which the alpha chain has been truncated. The inefficiency in antigen presentation can be amplified by pulsing the APC for 4 h with peptide rather than having peptide present throughout the presentation assay. Fixation of antigen-pulsed APC improves the capacity of APC with truncated class II molecules to stimulate T cell hybrids. Fixation of APC prior to exposure to antigen also leads to significant improvement in antigen presentation by the truncated class II molecules. Because the inefficiency of a given hybrid for antigen presentation does not correlate with its ability to transduce a signal as measured by protein kinase C translocation, we suggest that defects in this pathway are not the only cause of impaired antigen presentation. However, because previous studies have demonstrated the need for an intact cytoskeleton for successful antigen presentation, we propose that the carboxy truncated class II molecules are inefficient in antigen presentation because they are unable to generate the signal that ultimately leads to their interaction with the cytoskeleton. These observations underscore the complexity of the events that are required for achieving effective interactions between MHC class II molecules and TCR, and suggest, with regard to efficient antigen presentation, that the physical state of the class II molecules is at least as important as their signal transducing capacity.

Distinct structural compartmentalization of the signal transducing functions of major histocompatibility complex class II (Ia) molecules

Class II major histocompatibility complex encoded proteins (MHC class II or Ia molecules) are principal plasma membrane proteins involved in activation of both B and T cells during antigen-driven immune responses. Recent data indicate that class II molecules are more than simply recognition elements that provide a ligand for the T cell antigen receptor. Changes in B cell physiology that follow class II binding are now recognized as being required not only for the induction of T cell activation, but also for B cell activation and proliferation. It is interesting to note that class II molecules appear to transduce signals via two distinct mechanisms depending upon the differentiative state of the B cell on which they are expressed. While one of these pathways, involving cAMP generation and protein kinase C localization in the cytoskeletal/nuclear compartment, is seen in resting B cells, the second is seen in primed B cells and involves tyrosine kinase activation, inositol lipid hydrolysis, and Ca2+ mobilization. Use of this pathway is correlated with ability of class II to transduce signals leading to B cell proliferation. To begin to address the molecular basis of this unique, activation-dependent, differential coupling of class II to signaling pathways, we conducted mutational analysis of class II structural requirements for signal transduction. Here we report that the cytoplasmic (Cy) domains of I-Ak class II molecules are not required for either receptor-mediated activation of protein tyrosine phosphorylation or Ca2+ mobilization. This is in contrast to the requirement of the Cy domain of beta chain of class II for the alternate signaling pathway and efficient antigen presentation to autoreactive T cell lines. Disparate distribution of functional motifs within the MHC class II molecules may reflect use of distinct receptor associated effector molecules to sustain different modes of signal transduction in various class II-expressing cells.

Structural compartmentalization of MHC class II signaling function

Major histocompatibility complex (MHC) class II molecules are critical restricting elements in the generation of thymus-dependent immune responses. Recent studies indicate that in addition to providing a composite epitope for recognition by T-cell antigen receptors, MHC class II molecules function in signal transduction through interaction with other cellular proteins. Mutational analyses indicate that structural information necessary for these functions is compartmentalized in different aspects of the molecular complex. Here, William Wade and colleagues review the structural basis of this MHC class II function as defined in the I-A alpha and -beta chains.

Induction of costimulatory molecule B7 in M12 B lymphomas by cAMP or MHC-restricted T cell interaction

M12 B lymphomas expressing transfected Ak molecules with truncated cytoplasmic domains have a defect in Ag presentation to some autoreactive T cell hybrids. This defect in Ag presentation is corrected by pretreatment of the B cells with agents that elevate intracellular cAMP. Here we show that dibutyryl-cAMP treatment of M12 B lymphomas leads to cell surface expression of the costimulatory molecule B7. Furthermore, CTLA4Ig, a ligand for B7, inhibits activation of an accessory signal-dependent T hybrid. B7 is also inducible in M12 B lymphomas upon MHC-restricted interaction with T cells that can be activated by the APC, but not by T cells that fail to respond to truncated MHC-bearing M12 cells. Activation of the unresponsive T hybrids with immobilized anti-CD3 confers on them the ability to induce B7 in the APC. Direct engagement by immobilized antibodies of MHC class II on M12 B lymphomas did not induce B7 expression. Taken together, these results imply that during T-B interaction, initial T cell activation events lead to the ability of the T cell to induce costimulatory activity in the B cell, which in turn further activates the T cell. Activated T cell supernatants induced a small amount of B7 but were not nearly as effective as cAMP or as coincubation of T and B cells. These results suggest a role for T-B contact or localized cytokine secretion in the induction of B7 during T-B interaction.

Induction of costimulatory molecule B7 in M12 B lymphomas by cAMP or MHC-restricted T cell interaction

M12 B lymphomas expressing transfected Ak molecules with truncated cytoplasmic domains have a defect in Ag presentation to some autoreactive T cell hybrids. This defect in Ag presentation is corrected by pretreatment of the B cells with agents that elevate intracellular cAMP. Here we show that dibutyryl-cAMP treatment of M12 B lymphomas leads to cell surface expression of the costimulatory molecule B7. Furthermore, CTLA4Ig, a ligand for B7, inhibits activation of an accessory signal-dependent T hybrid. B7 is also inducible in M12 B lymphomas upon MHC-restricted interaction with T cells that can be activated by the APC, but not by T cells that fail to respond to truncated MHC-bearing M12 cells. Activation of the unresponsive T hybrids with immobilized anti-CD3 confers on them the ability to induce B7 in the APC. Direct engagement by immobilized antibodies of MHC class II on M12 B lymphomas did not induce B7 expression. Taken together, these results imply that during T-B interaction, initial T cell activation events lead to the ability of the T cell to induce costimulatory activity in the B cell, which in turn further activates the T cell. Activated T cell supernatants induced a small amount of B7 but were not nearly as effective as cAMP or as coincubation of T and B cells. These results suggest a role for T-B contact or localized cytokine secretion in the induction of B7 during T-B interaction.

Translational diffusion of class II major histocompatibility complex molecules is constrained by their cytoplasmic domains

Site-directed mutagenesis in vitro was used to introduce stop codons in the genomic DNA of the alpha and beta chains of the murine class II major histocompatibility complex antigen, I-Ak. Mutated DNA was transfected into B lymphoma cells that were then selected by neomycin resistance and for their ability to express I-Ak molecules on their plasma membrane. The translational diffusion coefficient (Dlat) of I-Ak molecules composed of a wild-type beta chain paired with an alpha chain missing either 6 or 12 amino acids from the cytoplasmic domain is on the average threefold higher than the Dlat of wild-type I-Ak molecules as measured by fluorescence photobleaching and recovery. The removal of 12 amino acids from the cytoplasmic domain of the beta chain did not change the Dlat value from that of wild-type I-Ak if the truncated beta chain was paired with a wild-type alpha chain. Removing all amino acids of the cytoplasmic domains of both the alpha and beta chains resulted in a 10-fold increase in the Dlat, the highest value for any of the truncated I-Ak molecules tested. These data indicate that the carboxy-terminal six amino acids of the cytoplasmic domain of the alpha chain and the six plasma membrane-proximal amino acids of the beta chain are important in constraining the translational diffusion of I-Ak molecules in the plasma membrane.

Altered I-A protein-mediated transmembrane signaling in B cells that express truncated I-Ak protein

Recent evidence suggests that the major histocompatibility complex class II molecules of B lymphocytes function as signal-transducing receptors during the generation of T lymphocyte-dependent humoral immune responses. By analogy with other receptors, we postulate that perturbation of the class II molecules is coupled to the generation of intracellular second messengers through interactions involving the transmembrane and/or cytoplasmic domains of the class II molecules. We report a series of experiments that assess which amino acids of the class II molecule I-Ak are required for coupling it to the signal-transduction pathway. We prepared a series of B-lymphocyte transfectants that express I-Ak molecules with COOH-terminal truncations of either the Ak alpha or Ak beta chain or both. The ability of each transfected class II molecule to transduce a signal after being bound by monoclonal antibody was found by monitoring the translocation of protein kinase C from the cytosol to the "nuclear compartment" of the transfected B lymphocyte. Results indicate that the Ak beta chain plays the dominant role in signal transduction and that the 6 cytoplasmic amino acids of Ak beta chain most proximal to the inner plasma membrane are of greatest importance in coupling I-Ak molecules to the molecules of the signaling cascade.

Antigen presentation abrogated in cells expressing truncated Ia molecules

Oligonucleotide site-directed mutagenesis was used to introduce a premature stop codon in wildtype A beta k and A alpha k cDNA clones to create truncated A beta k and A alpha k molecules lacking the cytoplasmic domain. Transfected B lymphoma cells expressing an I-Ak molecule with a truncated beta-chain or with truncated alpha- and beta-chains showed profound defects in two Ia-related functions: Ia-restricted Ag presentation and intracytoplasmic signaling. The ability of these transfected cell lines to activate autoreactive T hybrids was markedly impaired whereas loss of Ag presentation to nominal Ag-specific T hybrids was more subtle. Ia-mediated transmembrane signaling as measured by PKC translocation from cytosol to nucleus after stimulation with anti-Ak antibody was greatly affected by truncation of the A beta and A alpha cytoplasmic domains. These results indicate an important role for the highly conserved cytoplasmic domain in Ia-mediated responses.

Antigen presentation abrogated in cells expressing truncated Ia molecules

Oligonucleotide site-directed mutagenesis was used to introduce a premature stop codon in wildtype A beta k and A alpha k cDNA clones to create truncated A beta k and A alpha k molecules lacking the cytoplasmic domain. Transfected B lymphoma cells expressing an I-Ak molecule with a truncated beta-chain or with truncated alpha- and beta-chains showed profound defects in two Ia-related functions: Ia-restricted Ag presentation and intracytoplasmic signaling. The ability of these transfected cell lines to activate autoreactive T hybrids was markedly impaired whereas loss of Ag presentation to nominal Ag-specific T hybrids was more subtle. Ia-mediated transmembrane signaling as measured by PKC translocation from cytosol to nucleus after stimulation with anti-Ak antibody was greatly affected by truncation of the A beta and A alpha cytoplasmic domains. These results indicate an important role for the highly conserved cytoplasmic domain in Ia-mediated responses.

Immunochemical characterization of proteins from scrapie-infected hamster brain, using immunoblot analysis

Preparations of brain plasma membrane from scrapie-infected or noninfected hamsters were extracted with a solvent and were used to inoculate rabbits. Antisera evaluated by immunoblot analysis revealed a protein of 45 kD in scrapie-infected hamster brain that had a greater signal compared with proteins of comparable relative mass in noninfected brain. This 45-kD protein was not increased in scrapie-infected mouse, sheep, or goat brain. Seemingly, the 45-kD protein may be a degradation product of glial fibrillary acidic protein.

Effects of infection with Enterobacteriaceae enteropathogens on subsequent infection with Ascaris suum in the laboratory mouse

Prior to infection with Ascaris suum, ICR strain mice were inoculated with Salmonella typhisuis intraperitoneally or via gastric gavage. Similarly, Salmonella cholerae-suis var. kunzendorf, Salmonella typhimurium and enterotoxigenic Escherichia coli were administered to mice via gastric gavage 2 weeks prior to A. suum inoculation. Previous inoculation with S. typhisuis, via the intraperitoneal or gastric gavage routes and S. cholerae-suis var. kunzendorf decreased recovery of ascarid larvae from mice lungs. This effect appeared to be due to entrapment of migrating larvae by inflammatory reactions in the liver. This reaction was suspected to be due to non-specific resistance stimulated by the prior exposure to the bacterial pathogen. The number of A. suum larvae in the lungs of mice previously inoculated with S. typhimurium or enterotoxigenic E. coli (ETEC) was variable and in some cases greater in mice which had received the bacterial inoculation.

Effect of bacterial flora and mouse genotype (euthymic or athymic) on scrapie pathogenesis

Euthymic and athymic female BALB/c mice, reared under either germfree or defined flora conditions, were used to investigate the pathogenesis of scrapie after intracerebral or intraperitoneal inoculation. Time in days to onset of clinical signs (Stage I), to endstage (Stage II), and the time interval between Stage I and Stage II were compared among groups. In addition, scrapie agent titers in spleen were determined at 28 and 90 days after infection, as were agent titers in spleen and brain at Stage II. Three-way analysis of variance indicated that the bacterial flora, the presence or absence of a thymus, and the route of agent inoculation interact to produce significant differences in the pathogenesis of disease. The three factors in the experimental design also influenced the spleen titers of scrapie infectivity. The variation in scrapie pathogenesis among the groups of mice is likely to be mediated by differences in their reticuloendothelial systems. These differences may alter the agent's adsorption in spleen and/or route of transport from spleen to brain.

A tongue biopsy technique for the detection of trichinosis in swine

A tongue biopsy technique developed for the detection of Trichinella spiralis infection in swine involves taking a deep core biopsy of the tongue musculature, and examination of the sample by digestion. Using this procedure, 31 of 52 (60%) swine from an Indiana herd were found to be infected with T. spiralis. The average biopsy weighed 0.42 g, and the intensity of infection averaged 180 larvae per gram (range 2-1157). The biopsy was quick and easy to perform and the tongues healed well following the procedure. This technique may have applicability for Trichinella detection in epidemiological, control and research studies on swine and other animals.

Characterization of lipids in membrane vesicles from scrapie-infected hamster brain

The lipid compositions of membrane vesicles from scrapie-infected and uninfected hamster brains were examined before and after detergent extraction. No differences were observed in polar lipids, glycolipids, gangliosides or neutral lipids examined by thin-layer chromatography. Analysis of detergent-extracted CsCl gradient fractions with high scrapie infectivity failed to reveal any glycerolphosphatides, although neutral lipids were demonstrated. The major neutral lipid associated with detergent-extracted membrane vesicles from both infected and uninfected brain was an unidentified lipid which was found to absorb u.v. radiation strongly from 250 to 300 nm wavelengths. Membrane neutral lipids that strongly absorb u.v. radiation at wavelengths normally used to inactivate viruses may protect a small nucleic acid essential for scrapie infectivity.

Comparison of RNA from healthy and scrapie-infected hamster brain

Density gradient fractions prepared from healthy or scrapie-infected hamster brain tissue enriched in plasma membrane vesicles were treated with nucleases prior to phenol extraction and ethanol precipitation. The recovered nucleic acids were 3' end-labelled and run on one-dimensional polyacrylamide gels. Autoradiography revealed the presence of low molecular weight RNAs (4S) in both healthy and scrapie samples. Two-dimensional fingerprint analysis indicated that the RNAs isolated from scrapie-infected hamsters contained oligonucleotides that were not present in RNAs isolated from healthy hamsters.

Inactivation of the scrapie agent by ultraviolet irradiation in the presence of chlorpromazine

The sensitivity of the scrapie agent to u.v. inactivation was found to be related to the purity of the tissue preparation. Scrapie infectivity associated with membrane vesicles was unaffected when irradiated with 10(4) J/m2. Irradiation of more highly purified preparations from detergent-extracted CsCl gradient fractions reduced scrapie infectivity from 10(7.8) log10 LD50 per ml to as low as 10(4.5). Sensitivity of membrane-associated scrapie infectivity to inactivation by u.v. irradiation could be increased by addition of chlorpromazine, a phenthiazine antipsychotic which penetrates lipid bilayers and induces single-strand breaks in nucleic acids under irradiation. Chlorpromazine without irradiation, and a semiquinone protein-binding radical of chlorpromazine, failed to decrease scrapie infectivity by themselves. A closely related phenthiazine antipsychotic, trifluoperazine, which does not bind to nucleic acids, did not reduce scrapie infectivity. These findings suggest that the target of u.v. radiation for inactivation of scrapie infectivity in the presence of chlorpromazine is an essential nucleic acid.

Characterization of proteins in membrane vesicles from scrapie-infected hamster brain

Previous studies have shown that the scrapie agent is highly membrane-associated. We examined the protein composition of gradient fractions enriched for large membrane vesicles prepared from scrapie-infected and uninfected hamster brain using various methods to extract membrane proteins. We also examined proteins in detergent-extracted membrane vesicles fractionated on CsCl gradients. No qualitative differences in protein composition were seen comparing scrapie-infected and uninfected samples by one-dimensional gel electrophoresis. Extraction of proteins from membrane vesicles by phenol, pyridine, perchloric acid or lithium diiodosalicylate also failed to reveal any unique proteins in scrapie-infected hamster brain. Attempts to solubilize hydrophobic proteins (proteolipids) from CsCl gradient fractions into organic solvents were unsuccessful. These findings indicate that any hydrophobic protein associated with the scrapie agent is not a proteolipid, and that the ability of solvents to reduce scrapie infectivity is not a result of extraction of a proteolipid.

Equilibrium density gradient centrifugation of the scrapie agent in Nycodenz

Plasma membrane-enriched preparations from scrapie-infected and healthy hamster brains were detergent-extracted, then separated by equilibrium density centrifugation in continuous Nycodenz gradients. The highest level of infectivity was always associated with the insoluble residue which sedimented through 40% Nycodenz. The degree of aggregation in these insoluble complexes varied depending upon treatment. Centrifugation in gradients containing 2 M- to 8 M-urea resulted in the formation of large insoluble aggregates which seemed to retain a high level of infectivity when measured by the method of incubation interval assay. However, measurement of infectivity in these same samples by endpoint titration of tenfold dilutions resulted in values a thousand times lower. These observations reinforce previous findings that scrapie infectivity exists as a macromolecular complex and, furthermore, they emphasize the necessity for using non-denaturing conditions for purification of the scrapie agent.

Purification of the scrapie agent by density gradient centrifugation

Plasma membrane-enriched preparations from scrapie-infected and healthy hamster brains, as well as preparations of neural retina, were sonicated, then separated by rate-zonal sedimentation in 10 to 25% Nycodenz gradients. Gradient fractions were extracted with 0.5% Triton X-100 and re-fractionated by equilibrium density centrifugation in linear 25 to 40% CsCl gradients. Infectivity was highest in a fraction having a density of 1.280 g/ml and which contained a visible band of material. Digestion of the Nycodenz fractions with proteinase K before detergent extraction and CsCl fractionation resulted in a shift in the visible band to a density of 1.235 g/ml with most of the scrapie infectivity remaining at 1.280 g/ml. When labelled with 125I after 40-fold concentration, this 1.280 g/ml CsCl fraction from the proteinase K-treated gradients contained only a single band of protein(s) having a mol. wt. near 30 000. No differences were seen between proteins in healthy or scrapie-infected preparations.