A structural transition in class II major histocompatibility complex proteins at mildly acidic pH

Peptide binding by class II major histocompatibility complex proteins is generally enhanced at low pH in the range of hydrogen ion concentrations found in the endosomal compartments of antigen-presenting cells. We and others have proposed that class II molecules undergo a reversible conformational change at low pH that is associated with enhanced peptide loading. However, no one has previously provided direct evidence for a structural change in class II proteins in the mildly acidic pH conditions in which enhanced peptide binding is observed. In this study, susceptibility to denaturation induced by sodium dodecyl sulfate (SDS) detergent or heat was used to probe the conformation of class II at different hydrogen ion concentrations. Class II molecules became sensitive to denaturation at pH 5.5-6.5 depending on the allele and experimental conditions. The observed structural transition was fully reversible if acidic pH was neutralized before exposure to SDS or heat. Experiments with the environment-sensitive fluorescent probe ANS (8-anilino-1-naphthalene-sulfonic acid) provided further evidence for a reversible structural transition at mildly acidic pH associated with an increase in exposed hydrophobicity in class II molecules. IAd conformation was found to change at a higher pH than IEd, IEk, or IAk, which correlates with the different pH optimal for peptide binding by these molecules. We conclude that pH regulates peptide binding by influencing the structure of class II molecules.

Antigen unfolding and disulfide reduction in antigen presenting cells

CD4+ helper T cells recognize short peptides stably associated with class II MHC molecules displayed on the surface of antigen presenting cells. Very little is known about the sequence of events that lead to the generation of these peptides from protein antigens. It is likely that native proteins must partially unfold before they are cleaved by endopeptidases or bind to MHC proteins. For many antigens, the rate-limiting step in unfolding may involve reduction of disulfide bonds. Evidence that disulfide reduction occurs in endocytic compartments is reviewed and potential mechanisms for the reduction of antigen disulfide bonds are proposed.

Mechanisms of T cell epitope immunodominance analyzed in murine listeriosis

We demonstrate conclusively that the bacterial exotoxin listeriolysin O (LLO) is a target Ag for eliciting CD4+ T cell responses following infection with Listeria monocytogenes. The minimal I-Ek-restricted immunodominant CD4+ T cell epitope was identified as peptide 215-226 (p215-226). Most LLO-specific T cell hybridomas recognized p203-226, p208-226, p215-226, and p215-234, although each exhibited a characteristic pattern of preferential reactivity. One hybridoma (IIIC5) reacted to p203-226 but not to p208-226 or any other LLO peptide tested. With APCs from B10 congenic mice and cells transfected with either I-Ak or I-Ek, IIIC5 recognized p203-216 with I-Ak, while a different hybridoma (IB5) recognized p215-226 with I-Ek. Competitive binding studies demonstrated that of 15 LLO peptides tested, only p203-226, p215-226, and p215-234 had high affinity for I-Ek, while p203-226 could also bind to isolated I-Ak. Of nine LLO peptides tested, only p215-234 bound multiple class II MHC alleles. These findings suggest that the immunodominance of p203-226 may be due in part to the presence of multiple T cell epitopes with I-Ek- and I-Ak-binding capability. Many of the rules of immunodominance observed with model Ags are also operative in our murine model of bacterial infectious disease. Furthermore, a novel mechanism of immunodominance based on newly defined structural features of MHC molecules is implicated. This information is crucial for rational vaccine development.

Mechanisms of T cell epitope immunodominance analyzed in murine listeriosis

We demonstrate conclusively that the bacterial exotoxin listeriolysin O (LLO) is a target Ag for eliciting CD4+ T cell responses following infection with Listeria monocytogenes. The minimal I-Ek-restricted immunodominant CD4+ T cell epitope was identified as peptide 215-226 (p215-226). Most LLO-specific T cell hybridomas recognized p203-226, p208-226, p215-226, and p215-234, although each exhibited a characteristic pattern of preferential reactivity. One hybridoma (IIIC5) reacted to p203-226 but not to p208-226 or any other LLO peptide tested. With APCs from B10 congenic mice and cells transfected with either I-Ak or I-Ek, IIIC5 recognized p203-216 with I-Ak, while a different hybridoma (IB5) recognized p215-226 with I-Ek. Competitive binding studies demonstrated that of 15 LLO peptides tested, only p203-226, p215-226, and p215-234 had high affinity for I-Ek, while p203-226 could also bind to isolated I-Ak. Of nine LLO peptides tested, only p215-234 bound multiple class II MHC alleles. These findings suggest that the immunodominance of p203-226 may be due in part to the presence of multiple T cell epitopes with I-Ek- and I-Ak-binding capability. Many of the rules of immunodominance observed with model Ags are also operative in our murine model of bacterial infectious disease. Furthermore, a novel mechanism of immunodominance based on newly defined structural features of MHC molecules is implicated. This information is crucial for rational vaccine development.

A role for microfilaments but not microtubules in processing soluble antigens

Ag processing involves multiple intracellular membrane transport events required for delivery of Ag to degradative compartments in the endocytic pathway of antigen-presenting cells (APC) and transport of newly synthesized class II MHC proteins to compartments where peptide loading occurs. Movement and distribution of various subcellular vesicles have been shown to involve elements of the cytoskeletal network. We have examined the role of microtubules and microfilaments in Ag processing and presentation by B lymphoblastoid cells. Experiments with nocodazole or colchicine, drugs that disrupt the microtubule network, demonstrate that intact microtubules are not required for efficient processing of soluble Ag in these cells. Cytochalasins, which disrupt actin microfilaments, are observed to partially inhibit processing of soluble Ag. Inhibition is reversible and dependent on both the dose of drug and length of exposure. Control experiments demonstrate that the effect does not result from drug toxicity or decreased Ag uptake. Treatment of APC with cytochalasin B does not block delivery of internalized protein to dense lysosomes. However, the ability of the cells to catabolize internalized protein is partially inhibited. Our results suggest that microfilament-dependent, but not microtubule-dependent, vesicular transport may be required for efficient Ag processing in B lymphoblastoid cells.

Structural requirements of peptide and MHC for DR(alpha, beta 1*0401)-restricted T cell antigen recognition

We identified functionally important regions of the DR(alpha, beta 1*0401) peptide binding site and present a model of bound peptide. DR(alpha, beta 1*0401)-restricted T cell recognition and peptide binding of Mycobacterium leprae (ML) peptide 38-50 and overlapping peptides from the 18-kDa heat-shock protein were analyzed. ML38-50 is unusual in its restricted binding pattern, binding to only one of five DR4 subtypes and no other DR molecules tested. Amino acid substitutions were introduced into ML38-50 and the DR(alpha, beta 1*0401) peptide binding site at positions likely to influence peptide-MHC or peptide- or MHC-TCR interactions. Peptide binding, T cell proliferation, and computer modeling studies suggest that residues 39F, 42E, and 44D of ML38-50 interact with pockets 1, 4, and 6, respectively, of the peptide binding site. Only DR(alpha, beta 1*0401) substitutions at residues in pockets 4 or 7 prevented binding of ML38-50, while multiple substitutions at other positions negatively affected its T cell recognition. In contrast, T cell recognition of some high affinity ML peptides that overlapped ML38-50, and contained N-terminal extensions, was only abolished with pocket 4 substitutions. An inverse correlation of peptide affinity for DR(alpha, beta 1*0401) with negative effects of MHC substitutions on T cell recognition of the overlapping ML peptides was observed. Thus, some regions, such as pocket 4, dominantly influence T cell recognition of multiple DR(alpha, beta 1*0401)-binding peptides. However, each DR(alpha, beta 1*0401)-binding peptide appears to have unique properties that determine the outcome of its MHC-peptide interactions and the relative importance of other polymorphic pockets.

Structural requirements of peptide and MHC for DR(alpha, beta 1*0401)-restricted T cell antigen recognition

We identified functionally important regions of the DR(alpha, beta 1*0401) peptide binding site and present a model of bound peptide. DR(alpha, beta 1*0401)-restricted T cell recognition and peptide binding of Mycobacterium leprae (ML) peptide 38-50 and overlapping peptides from the 18-kDa heat-shock protein were analyzed. ML38-50 is unusual in its restricted binding pattern, binding to only one of five DR4 subtypes and no other DR molecules tested. Amino acid substitutions were introduced into ML38-50 and the DR(alpha, beta 1*0401) peptide binding site at positions likely to influence peptide-MHC or peptide- or MHC-TCR interactions. Peptide binding, T cell proliferation, and computer modeling studies suggest that residues 39F, 42E, and 44D of ML38-50 interact with pockets 1, 4, and 6, respectively, of the peptide binding site. Only DR(alpha, beta 1*0401) substitutions at residues in pockets 4 or 7 prevented binding of ML38-50, while multiple substitutions at other positions negatively affected its T cell recognition. In contrast, T cell recognition of some high affinity ML peptides that overlapped ML38-50, and contained N-terminal extensions, was only abolished with pocket 4 substitutions. An inverse correlation of peptide affinity for DR(alpha, beta 1*0401) with negative effects of MHC substitutions on T cell recognition of the overlapping ML peptides was observed. Thus, some regions, such as pocket 4, dominantly influence T cell recognition of multiple DR(alpha, beta 1*0401)-binding peptides. However, each DR(alpha, beta 1*0401)-binding peptide appears to have unique properties that determine the outcome of its MHC-peptide interactions and the relative importance of other polymorphic pockets.

DM enhances peptide binding to class II MHC by release of invariant chain-derived peptide

Major histocompatibility complex (MHC) class II molecules bind antigenic peptides rapidly after biosynthesis in antigen-presenting cells (APCs). By contrast, the rate of peptide binding to purified class II molecules is remarkably slow. We find that purified HLA-DR molecules bind peptides rapidly in the presence but not the absence of HLA-DM, a recently identified heterodimer required for efficient antigen processing. The same effect is seen with immunoprecipitated DM, suggesting that DM interacts directly with DR. Class II-associated invariant chain peptides (CLIP) are selectively and rapidly released from DR during incubation with DM at pH 5. We conclude that DM is a cofactor that enhances peptide binding to DR molecules through a mechanism involving peptide exchange.

[Reduction of traumatic primary anterior shoulder dislocation under local analgesia]

The aim of the present study was to evaluate the value of local versus intravenous anaesthesia in the reduction of acute shoulder dislocations. Patients with a primary traumatic dislocation of the shoulder were randomized to either local lidocaine or intravenous anaesthesia with pethidine/diazepam. The local method was performed with 20 ml of 1% lidocaine. The intravenous method was performed with pethidine/diazepam injected intravenously. The patients were observed for any complication during and after the procedure and the used methods were evaluated using a Visual Analogue Scale (VAS). In the period from November 1991 to September 1993 81 patients were admitted to our departments and 68 patients were included. Average age was 48 years (range 15-79) with 29 men and 39 women. Thirty-five patients were randomized to intravenous anaesthesia, 33 had a successful reduction and two failed. Thirty-three patients received local anaesthesia, 32 succeeded and one failed. Ten patients treated with the intravenous method had respiratory depression and six required antidote. No systemic or local side effects and no neuro-vascular injuries were recorded with the use of lidocaine. We did not observe any superficial or deep infection in the lidocaine group. There was no statistical difference between the average VAS value in the two groups. Local anaesthesia used to reduce acute primary anterior dislocation of the shoulder is a simple, safe and well-accepted method with significantly fewer respiratory complications.

The regulation of pH in resistance arteries from spontaneously hypertensive and Wistar-Kyoto rats: the effect of bicarbonate

OBJECTIVE

To assess intracellular pH regulation in the presence of bicarbonate in resistance arteries from spontaneously hypertensive rats and Wistar-Kyoto (WKY) rats.

METHODS

Intracellular pH was determined in isolated resistance arteries from male adults SHR and WKY rats with the pH-sensitive fluorescent dye bis-carboxyethyl carboxyfluorescein, while the arteries were mounted in a myograph for simultaneous measurements of force. The arteries were acid-loaded using the ammonium chloride technique and the recovery from the acidosis was determined in resting arteries and in arteries activated with 50 mmol/l potassium or arginine vasopressin. This protocol was performed in the presence and in the absence of bicarbonate.

RESULTS

In the absence of bicarbonate the intracellular pH was higher in resting arteries from SHR than in those from WKY rats, whereas during activation no significant difference was found. In the presence of bicarbonate no difference in intracellular pH between arteries from SHR and WKY rats could be found. The addition and washout of 15 mmol/l ammonium chloride were associated with large force transients in activated arteries both from SHR and from WKY rats. The proton recovery rate at intracellular pH 6.85 in the absence of bicarbonate was higher in activated arteries from SHR than in those from WKY rats, whereas in resting arteries no significant difference was found. In the presence of bicarbonate no significant difference between SHR and WKY rat arteries was found.

CONCLUSION

In the presence of bicarbonate a possible abnormality of the sodium-hydrogen exchange in resistance arteries from SHR is not manifested, because regulation of intracellular pH by bicarbonate-dependent mechanisms can compensate for such an abnormality.

Effects of tyrosine kinase inhibitors on the contractility of rat mesenteric resistance arteries

1. A pharmacological characterization of tyrosine kinase inhibitors (TKI) belonging to two distinct groups (competitors at the ATP-binding site and the substrate-binding site, respectively) was performed, based on their effects on the contractility of rat mesenteric arteries. 2. Both the ATP-site competitors (genistein and its inactive analogue, daidzein) and the substrate-site competitors (tyrphostins A-23, A-47 and the inactive analogue, A-1) reversibly inhibited noradrenaline (NA, (10 microM)) and KCl (125 mM) induced contractions, concentration-dependently. Genistein was slightly but significantly more potent than daidzein; the tyrphostins were all less potent than genistein, and there were no significant differences between the individual potencies. The tyrosine kinase substrate-site inhibitor bis-tyrphostin had no inhibitory effect. 3. Genistein, daidzein, A-23 and A-47 each suppressed the contraction induced by Ca2+ (1 microM) in alpha-toxin permeabilized arteries. A-1 and bis-tyrphostin had little or no effect on contraction of the permeabilized arteries. 4. Genistein was significantly more potent than daidzein with respect to inhibition of the contraction induced by 200 nM Ca2+ in the presence of NA (100 microM) and GTP (3 microM). The effect of A-23, A-47, A-1 and bis-tyrphostin was similar in permeabilized arteries activated with Ca2+ (200 nM) + NA (100 microM) + GTP (3 microM) and permeabilized arteries activated with 1 microM Ca2+. 5. Genistein (30 microM) reduced the fura-2 measured intracellular calcium activity ([Ca2+]j) in arteries stimulated with NA but had no effect on [Ca2+]i in arteries stimulated with KCl (125 mM).6. The potent effect of the TKIs in this study is consistent with a role for tyrosine kinases in the mechanisms which regulate both cytoplasmic Ca2+ levels and the effect of Ca2+ on the contractile apparatus in smooth muscle cells in resistance arteries. However, the results must be interpreted cautiously because the enzyme inhibitors may have a poor specificity in intact tissues and because the presumed inactive analogues had potent effects.

Electrical field stimulation of rat mesenteric small arteries: force and free cytosolic calcium during neurogenic contractions and mechanisms of non-neurogenic relaxations

The effect of transmural electrical field stimulation (TEFS) of rat mesenteric small arteries was studied. Stimulation parameters were selected to cause tetrodotoxin (TTX) sensitive contractions. In arteries precontracted with PGF2 alpha in the presence of phentolamine, TTX insensitive relaxation could be induced by TEFS. The relaxing effect of TEFS required higher stimulation amplitude and duration than the contractions. Thus, by appropriately choosing stimulation parameters, contractile responses could be elicited which were little affected by any relaxing effect, while contractions were abolished by TTX at any stimulation conditions in the present study. The contractions were abolished by cold storage and almost completely inhibited by phentolamine. Thus, contractions were neurogenic and primarily caused by noradrenaline. At low frequencies, TEFS caused phentolamine sensitive increases in free cytosolic calcium with no contractions. At higher frequencies, there was a further increase in free cytosolic calcium, associated with contraction. Only at high frequencies, noradrenaline from nerves caused sensitization of the contractile filaments to free cytosolic calcium as during stimulation with exogenous noradrenaline. The relaxations were associated with decreases in free cytosolic calcium and were probably non-neurogenic since they were resistant to TTX, cold storage, capsaicin, and repeated stimulation. Furthermore, relaxations were almost completely abolished by increasing extracellular potassium to 40 mM or by adding tetraethylammonium chloride or 4-aminopyridine. Relaxations were also reduced by ouabain and potassium free conditions.

Methanethiolation of the liberated cysteine residues of human alpha 2-macroglobulin treated with methylamine generates a derivative with similar functional characteristics as native alpha 2-macroglobulin

The thiol-modifying reagent methyl methanethiosulfonate reacts with the cysteine residues of thiol esters released upon treatment of human alpha 2-macroglobulin with methylamine. This methanethiolation generates a derivative of alpha 2-macroglobulin, with an 'open trap' and slow mobility in non-denaturing PAGE, similar to native alpha 2-macroglobulin. This similarity is further substantiated by surface hydrophobicity determinations and by the fact that neither the derivative nor native alpha 2-macroglobulin are cleared from the circulation in mice. Cleavages of bait regions in the derivative and native alpha 2-macroglobulin, however, result in electrophoretically fast forms which are cleared from the circulation in mice. In contrast to native alpha 2-macroglobulin, which can bind 2 mol chymotrypsin/mol, alpha 2-macroglobulin treated with methylamine and methylmethanethiosulfonate binds only 0.8 mol chymotrypsin/mol. Protection of trypsin against inhibition by soybean trypsin inhibitor is significantly better when alpha 2-macroglobulin is modified by methylamine and methylmethanethiosulfonate than when it is modified by dinitrophenyl thiocyanate, which cyanylates the exposed thiol group. The methanethiolated derivative is also more stable than the corresponding cyanylated derivative in that it is transformed to an electrophoretically fast form with a half-life of 9 h as compared to a half-life of 7 h for the latter. The transformation to the fast form is not due to instability of the thiol modification.

Reduction of traumatic secondary shoulder dislocations with lidocaine

The aim of the present study was to evaluate the value of local anaesthesia versus the commonly used intravenous pethidine/diazepam in the reduction of acute secondary shoulder dislocations. Patients with a traumatic secondary dislocation of the shoulder were randomized to either locally injected lidocaine or intravenously injected pethidine/diazepam. The local method was performed with 20 ml of 1% lidocaine. The patients were observed for any complication during and after the procedure, and the methods used were evaluated with a visual analogue scale (VAS). From November 1991 to September 1993, 62 patients were admitted to our departments of whom 52 were included in the study. Average age was 47 years (range 18-89 years) with 24 men and 28 women. Twenty-six patients were randomized to pethidine/diazepam; 22 had a successful reduction, and 4 were failures. Twenty-six patients received lidocaine, of whom 18 were successful and 8 not. Three patients treated with the intravenous method suffered respiratory depression, and one required an antidote. No systemic or local side-effects, no neurovascular damage and no early or late superficial or deep infection were recorded in the lidocaine group. There was no statistical difference between the average VAS value in the two groups. Lidocaine used to reduce acute secondary dislocations of the shoulder is a simple and safe method. It is as effective as the standard intravenous method and is well accepted by patients.

Structure and expression of a nitrite reductase gene from bean (Phaseolus vulgaris) and promoter analysis in transgenic tobacco

A structural gene encoding nitrite reductase (NiR) in bean (Phaseolus vulgaris) has been cloned and sequenced. The NiR gene is present as a single copy encoding a protein of 582 amino acids. The bean NiR protein is synthesized as a precursor with an amino-terminal transit peptide (TP) consisting of 18 amino acid residues. The bean NiR transit peptide shows similarity to the TPs of other known plant NiRs. The NiR gene is expressed in trifoliate leaves and in roots of 20-day old bean plants where transcript accumulation is nitrate-inducible. Gene expression occurs in a circadian rhythm and induced by light in leaves of dark-adapted plants. A particular 100 bp sequence is present in the promoter and in the first intron of the NiR gene. Several copies of this 100 bp sequence are present in the bean genome. Comparisons between the promoter of the bean NiR gene and of two bean nitrate reductase genes (NR1 and NR2) show a limited number of conserved motifs, although the genes are presumed to be co-regulated. Comparisons are also made between the bean NiR promoter and the spinach NiR promoter. Transformation of tobacco plants with the bean NiR promoter fused to the GUS reporter gene (beta-glucuronidase) shows that the bean NiR promoter is nitrate-regulated and that the presence of the 100 bp sequence influences the level of GUS activity. NiR-coding sequences are not required for nitrate regulation but have a quantitative effect on the measured GUS activity.

Minor role for direct adrenoceptor-mediated calcium entry in rat mesenteric small arteries

The role of membrane potential-dependent and independent regulation of the intracellular free calcium concentration ([Ca2+]i) was assessed in the mesenteric small arteries of Wistar rats. [Ca2+]i was determined by Fura-2 fluorescence. Membrane potential measurements were made using intracellular microelectrodes. Depolarization with a high-potassium solution (K-PSS) elevated [Ca2+]i and induced contraction. Further addition of 10 microM noradrenaline (NA) did not elevate [Ca2+]i further but enhanced tone. Addition of calcium channel inhibitors (felodipine or D-600) inhibited the maintained rise in [Ca2+]i with K-PSS, but NA still elevated [Ca2+]i and force to about half the previous level. Further addition of either ryanodine or thapsigargin eliminated the rise in [Ca2+]i with NA, although 10-20% of the contraction remained. Simultaneous measurements of membrane potential, [Ca2+]i, and force during cumulative additions of NA or K-PSS in the absence of inhibitors showed similar relations between membrane potential and [Ca2+]i for each means of activation. The results indicate that membrane potential and [Ca2+]i are strongly correlated in mesenteric small arteries. A small part of the [Ca2+]i increase to NA can be attributed to release from intracellular stores. Membrane potential-independent calcium channels that are directly operated by adrenoceptors appear to play a minor role in the regulation of [Ca2+]i in these vessels.

Reduction of traumatic, primary anterior shoulder dislocations with local anesthesia

This study evaluates the use of local anesthesia in the reduction of acute shoulder dislocations. Patients with a primary traumatic dislocation of the shoulder were randomly assigned to receive either local anesthesia or intravenous anesthesia. The patients were observed for any complication during and after the procedure, and the methods used were evaluated with a visual analog scale. In the period from November 1991 to September 1993, 81 patients were admitted to our departments, and 68 patients were included in the study. Average age was 48 years (range 15 to 79 years); 29 men and 39 women were studied. Thirty-five patients were randomly assigned to receive intravenous anesthesia; 33 had a successful reduction, and two had a failed reduction. Thirty-three patients received local anesthesia; 32 had a successful reduction, and one had a failed reduction. Ten patients treated with the intravenous method had respiratory depression, and six required an antidote. No systemic or local side effects and no neurovasculor injuries were recorded. We did not observe any superficial or deep infection in the local anesthetic group. No statistical difference was found between the average visual analog value scale in the two groups. Local anesthesia to reduce acute primary anterior dislocation of the shoulder is a simple and safe method.

Requirement for protein synthesis in antigen processing by B cells

The role de novo protein synthesis plays in Ag processing by B cells was investigated. Cycloheximide (CHX) inhibited Ag processing in normal and transformed B cells. B lymphoblastoid cells required a 2-6 hr longer CHX pretreatment period than splenic B cells to inhibit Ag processing function. Immunoprecipitation experiments demonstrated that the half-life of class II/invariant chain (Ii) complexes was similar in normal and transformed B cells. B lymphoblastoid cells differed from splenic B cells in that a significant fraction of total class II-associated p31 Ii was modified with sialic acid (Ip). The kinetics of loss of class II-associated Ip in CHX-treated cells correlated with loss of Ag processing function. In addition, the half-life of a subpopulation of class II molecules that are unstable in sodium dodecyl sulfate at room temperature was greater in transformed cells. Our results suggest that B lymphoblastoid cells, but not splenic B cells, contain a long-lived pool of class II/Ii complexes that can bind and present peptides generated in endosomal compartments for a significant time period after cessation of protein synthesis.

Binding of lipoprotein lipase to alpha 2-macroglobulin

The interaction between bovine lipoprotein lipase (bLPL) and human alpha 2-macroglobulin (alpha 2M) was studied by use of non-denaturing PAGE and gel-permeation, Zn(2+)-Sepharose and heparin-Sepharose chromatography. It was demonstrated that bLPL in vitro binds non-covalently to native alpha 2M, but not to the receptor-recognized form produced by treatment of alpha 2M with chymotrypsin or methylamine. A small amount of bLPL was bound covalently to alpha 2M by disulphide interchange, when incubated together with chymotrypsin or methylamine. Whereas alpha 2M in complex with bLPL still bound to Zn(2+)-Sepharose, bLPL lost the ability to bind to heparin-Sepharose. Preincubation of bLPL with heparin prevented complex-formation with alpha 2M, suggesting that alpha 2M interacts with the heparin-binding domain of bLPL. Experiments in which 125I-bLPL was incubated with human plasma at 20 degrees C demonstrated an 11-17% binding of the labelled lipase to alpha 2M, indicating that this interaction may be of physiological significance.

Use of hydrophobic affinity partitioning as a method for studying various conformational states of the human alpha-macroglobulins

The serum proteins alpha 2-macroglobulin and pregnancy zone protein undergo major conformational changes when complexed with proteinases. It is shown that the changes in delta log Kmax determined by hydrophobic affinity partitioning is a measure of the extent of changes in the conformation of these alpha-macroglobulins. We introduce a new term for the changes of surface hydrophobicity in a protein as delta log Kacc. This defines the difference of delta log Kmax between a modified and an unmodified conformational state of a specific protein and can be useful as a parameter to describe the apparent conformational changes in the protein.

Membrane interactions influence the peptide binding behavior of DR1

We analyzed the binding of an influenza matrix protein-derived peptide, MAT(17-31), to cell surface and purified DR1. The pH dependence of peptide binding was dramatically influenced by the membrane environment. Cell surface binding was enhanced at low pH, with little or no binding detected at neutral pH and optimal binding at pH 4. By contrast, hydrogen ion concentration had minimal effect on peptide binding to purified DR1. Exposure to low pH in the absence of peptide did not affect the peptide binding capacity of cell-associated DR1. Purified DR1 was stable at low pH, excluding the possibility that enhanced binding was offset by a competing denaturation event at low pH. The striking effect of pH on peptide binding characteristic of cell surface DR1 was recovered after reconstitution of purified DR1 in B cell membranes by detergent dialysis. This behavior was partially recovered by reconstitution of full-length, but not truncated DR1 in vesicles containing purified lipid. Our results demonstrate that interactions involving membrane components influence the peptide-binding behavior of DR1.

Probing different conformational states of pregnancy-zone protein. Fluorescence studies utilizing the binding of 4,4'-bis(8-anilino-1-naphthalenesulphonate)

The binding of the fluorescence probe 4,4'-bis(8-anilino-1-naphthalenesulphonate) (bis-ANS) to the human proteinase inhibitor pregnancy-zone protein (PZP) and its complexes with methylamine and chymotrypsin were investigated. The existence of dimeric PZP-chymotrypsin complex was demonstrated and both the dimeric and the tetrameric PZP-chymotrypsin complexes could be studied separately. The fluorescence data indicate that bis-ANS binds to two different sites on PZP and its complexes. The values of the dissociation constant, Kd1, for the binding to the high-affinity site were determined to be 231 +/- 14, 220 +/- 28, 114 +/- 15 and 49 +/- 1 nM, for the binding to native PZP, PZP-methylamine and dimeric and tetrameric PZP-chymotrypsin, respectively. An 11-30-fold decrease was observed in the affinity for the second site, the corresponding values of the dissociation constant, Kd2, being 1.5-2.8 +/- 1.0 microM, which are not significantly different for PZP and its derivatives. The results suggest that the probe bis-ANS discriminates between the different conformational states of PZP and that while the conformation of the complex with methylamine does not differ much from that of the native protein, there is a significant change in conformation when chymotrypsin cleaves the bait region. This is substantiated by a 30%-45% decrease in the maximum enhancement of fluorescence intensity when PZP is treated with chymotrypsin. Although the dimeric and tetrameric forms of PZP-chymotrypsin complexes differ in Kd1 values, the difference in the maximum enhancement of the fluorescence of bis-ANS by the two forms is not significant. This indicates that dimer-dimer interaction in the tetrameric form does not involve hydrophobic sites. The necessity of bait-region cleavage for extensive conformational changes in PZP distinguishes it from alpha 2-macroglobulin, the other alpha-macroglobulin in human plasma.

Spike generating smooth muscle cells in mesenteric artery of rats

Membrane electrical properties of smooth muscle cells at different loci in the vessel wall of rat small mesenteric arteries were studied using glass microelectrodes. Isometric force was measured simultaneously. Penetrations of smooth muscle cells on the adventitial side (outer cells) showed an average resting potential, -43.1 +/- 0.8 mV (n = 24). In outer cells, numerous depolarizing junctional potentials and, to a lesser degree, hyperpolarizing junctional potentials were observed. When current was injected, electrotonic potentials were recorded. Input resistance was 2.2 +/- 0.1 x 10(9) omega (n = 15), suggesting that the low resistance pathways commonly observed in smooth muscle tissue are absent among these cells. Transmural electrical stimulation of nerves elicited spikes and summation of junctional potentials, accompanied by force. TTX virtually abolished these effects of the transmural stimulation. In contrast, cells near the intima (inner cells) had an average resting potential of -65.8 +/- 0.9 mV (n = 37). No spontaneous electrical activity was observed; nor could electrotonic potentials be recorded. Thus, the smooth muscle cells from the outer layer of rat small resistance arteries differ from the inner cells in their lower membrane potentials, generation of spikes, higher input resistance and innervation. Results also suggest that the influence of nerves may be to facilitate opening of voltage-gated Ca2+ channels in innervated cells.

A europium fluoroimmunoassay for measuring binding of antigen to class II MHC glycoproteins

A dissociation-enhanced lanthanide fluoroimmunoassay employing europium-streptavidin and time-resolved fluorimetry was developed to measure binding of biotin-labeled peptides to class II MHC proteins. Binding of biotin-peptides as measured by this assay was saturable and inhibited in the presence of unlabeled peptide. Background fluorescence was minimal and there was a direct relationship between signal and biotin-peptide/class II complex concentration from 1.3 pmol to less than 1 fmol total class II. The sensitivity of the assay and the ability to selectively capture specific class II proteins from detergent lysates of cells with solid phase mAb made it possible to measure formation peptide/class II complexes in live APC cultured with biotin-labeled insulin. This assay is expected to be useful for routine measurement of peptide/class II binding and biochemical analysis of Ag processing events.

Free cytosolic Ca2+ measured with Ca(2+)-selective electrodes and fura 2 in rat mesenteric resistance arteries

Free cytosolic Ca2+ was measured with sub-micrometer-tip, double-barrelled, Ca(2+)-selective electrodes and fura 2 in rat mesenteric resistance arteries. The purpose was to establish intracellular free Ca2+ concentration ([Ca2+]i) values in resting and stimulated vessels. Isolated vessels were mounted for isometric force measurements. Measured with electrodes, mean [Ca2+]i was 115 and 708 nM under resting and norepinephrine-activated conditions, respectively. Fura 2 was calibrated intracellularly including determination of the intracellular dissociation constant (Kd) of the fura 2:Ca2+ complex. The intracellular Kd was 342 nM. With this value of Kd, fura 2 measurements of mean [Ca2+]i were 129 and 537 nM under resting and norepinephrine-activated conditions, respectively. The values measured with the two techniques were thus in good accordance.

Force, membrane potential, and [Ca2+]i during activation of rat mesenteric small arteries with norepinephrine, potassium, aluminum fluoride, and phorbol ester. Effects of changes in pHi

In activated rat mesenteric small arteries, the effect of pHi on force, membrane potential, and free cytosolic calcium ([Ca2+]i) was assessed. Arteries were mounted in a myograph for isometric force development, and [Ca2+]i, pHi, or membrane potential was measured simultaneously with force. During activation with norepinephrine, potassium, aluminum fluoride (AlF-4), and phorbol 12-myristate 13-acetate (PMA, a phorbol ester), the vessels depolarized and [Ca2+]i increased, although the ratio of force to [Ca2+]i was less during potassium activation than with the other types of activation. Changes in pHi, with a constant pHo, were induced with NH4Cl or by changing PCO2. In resting vessels, the effects of the changes in pHi on tension, membrane potential, and [Ca2+]i were negligible. In vessels activated with norepinephrine or AlF-4, alkalinization caused an acute decrease of tone, which could be explained by a decrease in [Ca2+]i consequent to repolarization of the membrane. In vessels activated with potassium or PMA, the effects of alkalinization were smaller. This is consistent with acute alkalinization, affecting steps proximal in the excitation-contraction coupling distal to activation of G proteins. Acidification caused a transient increase in tone and [Ca2+]i, irrespective of the mode of stimulation, without affecting the membrane potential. Ryanodine did not abolish the transient increase in tone and [Ca2+]i. Thus, acute intracellular acidification may induce tone by release of an intracellular ryanodine-insensitive calcium pool or by affecting transmembranal calcium flux although in a membrane potential-independent way.

Comparison of conformational changes of pregnancy zone protein and human alpha 2-macroglobulin, a study using hydrophobic affinity partitioning

Conformational changes of human alpha 2-macroglobulin (alpha 2M) and pregnancy zone protein (PZP), reflected in changes in surface hydrophobicity, have been studied. The results show that the conformation of alpha 2M is governed by the degree of 'trapping'. Thus, cleavage in the bait region and of the thiol ester by proteinase treatment causes a two-fold increase in surface hydrophobicity of alpha 2M. However, the increase is still higher (three-fold) when the thiol esters in alpha 2M alone are cleaved by methylamine. Cyanylation of the thiol groups exposed upon methylamine treatment yields a derivative with the same hydrophobicity as native alpha 2M. Treatment of this derivative with chymotrypsin restores the hydrophobicity to that of methylamine-treated alpha 2M. Since the C-terminal 18 kDa fragment of alpha 2M exhibits no hydrophobicity, the change in hydrophobicity seems not to reside in the receptor binding site. In contrast to alpha 2M, modification of both native and methylamine-treated PZP with chymotrypsin gives a reduction (about 40%) in hydrophobicity. The change in hydrophobicity is insignificant on treatment with methylamine alone. Furthermore, hydrophobic interactions appear not to contribute to tetramerization of PZP. The present study indicates major differences in the conformational states of alpha 2M and PZP as reflected in the hydrophobic surfaces exhibited.

Acidification and disulfide reduction can be sufficient to allow intact proteins to bind class II MHC

The hypothesis that reduction of disulfide bonds and exposure to low pH may be sufficient to allow intact proteins to bind class II MHC was addressed in this study. Functional assays were used to determine minimal conditions sufficient to bypass the requirement for Ag processing. Fixed APC, pulsed with HEL at pH 5 in the presence of a reducing agent, were observed to stimulate I-Ed-restricted T cell hybridomas. Activity required both low pH and reducing agent. Fixed APC also stimulated cytochrome c-specific T cells after exposure to Ag at pH 5 but not pH 7. No reducing agent was required. Peptide was considerably more potent in these assays than intact cytochrome c. By contrast, highly purified cytochrome c was equal in potency with a peptide in competition binding assays using purified I-Ek. The protein did not bind I-Ad or I-Ak. This suggested that cytochrome c can efficiently bind I-Ek at low pH without the requirement for proteolytic cleavage. The capacity of HEL to bind purified I-Ed was strictly dependent on the presence of reducing agent. The reducing agent alone had no effect. A small panel of proteins was screened for class II binding at low pH in competition assays. Horse myoglobin and human hemoglobin were particularly potent in their capacity to inhibit binding of biotin-labeled peptide to purified class II. Unlabeled peptide inhibited binding of labeled peptide to I-Ad at pH 5 and pH 7. By contrast, intact horse myoglobin was active only at pH 5. This result suggested that low pH may enhance the binding of horse myoglobin to I-Ad through effects on the structure of both proteins. Our observations support the hypothesis that low pH and disulfide reduction can be sufficient to allow partially unfolded or structurally destabilized proteins to bind class II MHC.

Acidification and disulfide reduction can be sufficient to allow intact proteins to bind class II MHC

The hypothesis that reduction of disulfide bonds and exposure to low pH may be sufficient to allow intact proteins to bind class II MHC was addressed in this study. Functional assays were used to determine minimal conditions sufficient to bypass the requirement for Ag processing. Fixed APC, pulsed with HEL at pH 5 in the presence of a reducing agent, were observed to stimulate I-Ed-restricted T cell hybridomas. Activity required both low pH and reducing agent. Fixed APC also stimulated cytochrome c-specific T cells after exposure to Ag at pH 5 but not pH 7. No reducing agent was required. Peptide was considerably more potent in these assays than intact cytochrome c. By contrast, highly purified cytochrome c was equal in potency with a peptide in competition binding assays using purified I-Ek. The protein did not bind I-Ad or I-Ak. This suggested that cytochrome c can efficiently bind I-Ek at low pH without the requirement for proteolytic cleavage. The capacity of HEL to bind purified I-Ed was strictly dependent on the presence of reducing agent. The reducing agent alone had no effect. A small panel of proteins was screened for class II binding at low pH in competition assays. Horse myoglobin and human hemoglobin were particularly potent in their capacity to inhibit binding of biotin-labeled peptide to purified class II. Unlabeled peptide inhibited binding of labeled peptide to I-Ad at pH 5 and pH 7. By contrast, intact horse myoglobin was active only at pH 5. This result suggested that low pH may enhance the binding of horse myoglobin to I-Ad through effects on the structure of both proteins. Our observations support the hypothesis that low pH and disulfide reduction can be sufficient to allow partially unfolded or structurally destabilized proteins to bind class II MHC.

The efficacy of Na-naproxen after diagnostic and therapeutic arthroscopy of the knee joint

The purpose of the study was to evaluate the effect of na-naproxen after diagnostic arthroscopy and arthroscopic surgery of the knee joint. In a double-blind trial, 41 patients were randomized to treatment with na-naproxen, and 46 patients were given placebo after surgery. For additional analgesia, patients got acetaminophen if necessary. In patients who underwent arthroscopic surgery, there were no differences between those treated with na-naproxen and those who received placebo in pain levels, but patients receiving na-naproxen had significantly less need for additional analgesia and returned significantly more quickly to work than patients receiving placebo (median 10 versus 30 days). In patients who had only diagnostic arthroscopy, there were no differences between the na-naproxen and placebo groups.

Differences in the proteinase inhibition mechanism of human alpha 2-macroglobulin and pregnancy zone protein

Different conformational states of human alpha 2-macroglobulin (alpha 2M) and pregnancy zone protein (PZP) were investigated following modifications of the functional sites, i.e. the 'bait' regions and the thiol esters, by use of chymotrypsin, methylamine and dinitrophenylthiocyanate. Gel electrophoresis, mAb (7H11D6 and alpha 1:1) and in vivo plasma clearance were used to describe different molecular states in the proteinase inhibitors. In alpha 2M, in which the thiol ester is broken by binding of methylamine and the 'trap' is closed, cyanylation of the liberated thiol group from the thiol ester modulates reopening of the 'trap' and the 'bait' regions become available for cleavage again. The trapping of proteinases in the cyanylated derivative indicates that the trap functions as in native alpha 2M. In contrast, cyanylation has no effect on proteinase-treated alpha 2M. As demonstrated by binding to mAb, the methylamine and dinitrophenylthiocyanate-treated alpha 2M exposes the receptor-recognition site, but the derivative is not cleared from the circulation in mice. The trap is not functional in PZP. In native PZP and PZP treated with methylamine, the conformational states seem similar. The receptor-recognition sites are not exposed and removal from the circulation in vivo is not seen for these as for the PZP-chymotrypsin complex. Tetramers are only formed when proteinases can be covalently bound to the PZP. Conformational changes are not detected in PZP derivatives in which the thiol ester is treated with methylamine and dinitrophenylthiocyanate. The results suggest that the conformational changes in alpha 2M are generated by mechanisms different to these in PZP. The key structure gearing the conformational changes in alpha 2M is the thiol ester, by which the events 'trapping' and exposure of the receptor-recognition site can be separated. In PZP, the crucial step for the conformational changes is the cleavage of the 'bait' region, since cleavage of the thiol ester does not lead to any detectable conformational changes by the methods used.

[Physical causes of accidental falls among the elderly in their own homes]

Accidental falls in elderly persons involve considerable illness and great hospital costs. During the period 1971-1986, the incidence has risen from 14 to 19 per 1000 annually. Four hundred and seventy-three individuals aged 60 years or more who had fallen in their own homes and who sought help in Odense Hospital after the accident were interviewed consecutively. The replies to these interviews described the circumstances involved in the fall together with the health and social conditions. Women constituted 78% of the material with preponderance of people living alone as compared with the background population. Just under half of the patients had had a previous fall. Fractures were sustained in 40% of the cases. In 51% of the cases, a definite or probable external circumstance was the cause of the fall. In 150 out of 237 accidental falls, caused by external circumstances, the accident was considered to have been preventable by means of eg more accessible lighting, non-slip carpeting, removal of doorsteps, more suitable arrangement of furniture and better supportive measures beside stairs. The risk of falling is found to increase markedly in persons aged 75 years or more. Prophylactic measures are recommended before patients reach this age by means of information to elderly persons and to persons involved in home care about situations involving risks.

Long-lived complexes between peptide and class II major histocompatibility complex are formed at low pH with no requirement for pH neutralization

The binding of peptide antigens to class II histocompatibility glycoproteins can be markedly enhanced at pH values approximating those found in acidic endosomal compartments in antigen-presenting cells (APC). It has been proposed by others that low pH may increase the conformational flexibility of class II, facilitating both the association and dissociation of peptides. Neutralization of pH, as class II is expressed on the plasma membrane of APC, could then serve to trap peptide in a stable complex. If this were the only mechanism accounting for enhanced peptide binding at low pH, one would predict that there should be a concordance between the pH conditions required for enhanced binding and those associated with increased peptide dissociation. Furthermore, long-lived complexes of class II and peptide should not be observed at low pH without neutralization. In the present communization, I provide the data that support the generality of my previous conclusion that both affinity and maximal binding are regulated by pH in experiments using purified class II and biotin-labeled peptides. The pH profile for binding and dissociation using three different class II glycoproteins was analyzed, and the results demonstrated that enhanced binding is not coupled to enhanced dissociation. Peptide complexes were observed to be quite stable at pH 4.5 and above. This result was further substantiated in experiments where biotin-peptide/class II complexes were extensively dialyzed at low pH followed by analysis on Western blots probed with avidin. Finally, a low pH assay system was devised to analyze the formation of stable peptide/class II complexes without pH neutralization. Our results indicate that stable complexes can be formed at low pH without the requirement for a shift to neutral pH.

Endogenous and exogenous agonist-induced changes in the coupling between [Ca2+]i and force in rat resistance arteries

The relationship between isometric tension and free cytoplasmic calcium, [Ca2+]i, was investigated in rat isolated resistance arteries using fura-2. Depolarisation with 125 mM K+ induced a tonic contraction, while [Ca2+]i increased transiently but stabilised above resting [Ca2+]i. Furthermore, the tension/[Ca2+]i ratio was lower during activation with 125 mM K+ if the effect of endogenous noradrenaline (NA) was inhibited. Concentration/response curves with NA and K+ indicated that NA increased the sensitivity to [Ca2+]i. Calcium concentration/response curves in the presence of 10 microM NA or 125 mM K+ showed that NA could induce force at or below resting [Ca2+]i, while for any given bath calcium concentration, [Ca2+]i was similar in the presence of NA or K+. Addition of NA or vasopressin (AVP) to vessels depolarised with 125 mM K+ caused force development but no increase in [Ca2+]i, suggesting that agonists increase the efficacy of [Ca2+]i. However, during activation with AVP the efficacy of [Ca2+]i decreased time-dependently. The results suggest that in resistance arteries [Ca2+]i plays a crucial role in excitation-contraction coupling, but the tension/[Ca2+]i relationship can be modified by exogenous and endogenous agonists.

Malignant phyllodes tumor of the prostate. A case report with immunohistochemical and ultrastructural studies

Phyllodes tumor of the prostate is a rare neoplasm with cellular or sarcomatoid stroma and hyperplastic glands. This lesion shares many histologic features with cystosarcoma phyllodes of the breast. Although a malignant variant of phyllodes tumor of the prostate has been described, the majority of cases have been clinically benign. We report an unusual case of phyllodes tumor of the prostate in which the stromal component underwent malignant degeneration, a finding not previously described (to our knowledge). Immunohistochemical and ultrastructural studies demonstrated smooth-muscle differentiation of the stromal cells.

Reduction of disulfide bonds during antigen processing: evidence from a thiol-dependent insulin determinant

Previous studies have demonstrated that insulin, like other protein antigens, requires processing in metabolically active antigen-presenting cells (APC) before it can be recognized by class II-restricted T lymphocytes. Unlike many other proteins, insulin peptides of minimal size retain the requirement for antigen processing. We demonstrate that this requirement can be bypassed by incubation of insulin with reducing agents in the presence of aldehyde-fixed APC. Fixed APC treated in this way were able to stimulate I-Ab- and I-Ad-restricted T cell hybridomas. Data are presented that demonstrate that cloned and polyclonal T cells recognize a determinant within the NH2-terminal 14 residues of the beef insulin A chain with no requirement for B chain residues. The common feature among peptides capable of stimulating these cells in the presence of live APC is the chemical form of the cysteine thiol groups. Those forms that produce free thiols upon reduction are active, whereas those with irreversibly protected sulfhydryls are not. Functional experiments with fixed APC and competition binding experiments with purified I-Ad indicate that only A chain peptides with free thiols are able to stably associate with the peptide-binding site on class II in a form that is recognized by specific T cells. Our findings indicate that reduction of disulfide bonds is both necessary and sufficient for presentation of insulin to a major population of class II-restricted T cells. The results provide strong support for the hypothesis that protein disulfides can be reduced during physiologic antigen processing.

Enhanced binding of peptide antigen to purified class II major histocompatibility glycoproteins at acidic pH

Helper T lymphocytes recognize peptide antigens stably associated with class II major histocompatibility complex (MHC) glycoproteins on the surface of antigen-presenting cells and serve to regulate a wide variety of immune responses. A previous study from our laboratory had demonstrated that the functional association of various peptide antigens with the antigen-presenting cell membrane was increased at pH 5 as compared to pH 7, consistent with the potential role of acidic endosomal compartments in antigen processing. The mechanism for this effect was not determined. In the present study, assays using purified class II glycoprotein were used to further define this mechanism. The potential requirement for pH-dependent interactions involving non-MHC membrane components was excluded in functional assays with purified class II reconstituted in artificial membranes containing only neutral phospholipids and cholesterol. The association of HEL(104-120) with I-Ed, and OVA(323-339) with I-Ad, was increased at pH 5, as measured by activation of specific T cell hybridomas. An enzyme immunoassay was developed to measure the binding of biotin-labeled peptides to purified class II in detergent micelles. The pH dependence of binding paralleled our previous functional results. Optimum binding of biotin-HEL(104-120) to I-Ed was observed at pH approximately 4.5, whereas maximum binding of biotin-Myo(106-118) to I-Ad occurred at pH approximately 5.5. The latter peptide also bound weakly to I-Ed, but with a pH dependence similar to that observed using HEL(104-120). Further experiments with biotin-HEL(104-120)/I-Ed indicated that both the apparent affinity and the apparent concentration of peptide-binding sites are increased as hydrogen ion concentration is increased from pH 7 to pH 5. The effect of pH in this range was largely reversible and was not associated with a change in peptide dissociation that could be measured with our assay system. Binding was not inhibited in the presence of 1.5 M NaCl, suggesting that electrostatic interactions between HEL(104-120) and I-Ed are not essential for binding. It is proposed that protonation of a critical group(s) in the class II molecule regulates its capacity to form stable complexes with peptide. However, this effect alone does not fully account for the rapid kinetics of peptide binding observed in experiments with intact antigen-presenting cells.

T cells from nonresponder mice. MHC restricted and unrestricted recognition of insulin

Two types of insulin-reactive T cell hybridomas expressing TCR-alpha beta were derived from nonresponder H-2b mice immunized with pork insulin. One type had characteristics of conventional class II-restricted Th cells. These CD4+ CD8- I-Ab-restricted T cells recognized a self determinant, present within the insulin B-chain. This determinant was distinct from the immunodominant A-chain loop determinant that is recognized by the majority of T cells induced after immunization with normally immunogenic beef insulin. Our results suggest that this determinant is readily generated during immunologic processing of insulins, including nonimmunogenic pork insulin and self insulin. A second type of T cell lacking CD4 and CD8 recognized a distinct B-chain determinant of insulin in a class II-dependent, but MHC unrestricted, fashion. These cells may represent a novel subpopulation which has bypassed conventional selection during development in the thymus.

T cells from nonresponder mice. MHC restricted and unrestricted recognition of insulin

Two types of insulin-reactive T cell hybridomas expressing TCR-alpha beta were derived from nonresponder H-2b mice immunized with pork insulin. One type had characteristics of conventional class II-restricted Th cells. These CD4+ CD8- I-Ab-restricted T cells recognized a self determinant, present within the insulin B-chain. This determinant was distinct from the immunodominant A-chain loop determinant that is recognized by the majority of T cells induced after immunization with normally immunogenic beef insulin. Our results suggest that this determinant is readily generated during immunologic processing of insulins, including nonimmunogenic pork insulin and self insulin. A second type of T cell lacking CD4 and CD8 recognized a distinct B-chain determinant of insulin in a class II-dependent, but MHC unrestricted, fashion. These cells may represent a novel subpopulation which has bypassed conventional selection during development in the thymus.

Immunogenicity of B chain in insulin responder and nonresponder mice

The potential immunogenicity of insulin B chain in beef insulin low-responder H-2k,a and high-responder H-2b,d mice was examined using lymph node proliferation assays. Oxidized B chain was immunogenic in H-2k,a, but not H-2b,d, mice. The T cell population recognized a determinant in OX-B chain associated with I-Ak. These cells did not respond to intact insulin, suggesting that the B chain determinant was not available to I-Ak during immunologic processing of insulin. Responses were observed in H-2k and H-2d, but not H-2b, after immunization with reduced and carboxyamidomethylated-insulin which contains equimolar A chain and B chain. These responses were I-A-restricted and heterogeneous, with reactivity to A chain and B chain determinants. In each case, little or no cross-reactivity was observed between RCAM-insulin and intact insulin. Furthermore, T cell populations induced in H-2k mice selectively recognized OX-B chain or RCAM-B chain, which differ in chemical modification of the thiols of Cys B7 and Cys B19. Similarly, RCAM-BINS-immune T cells from H-2d did not react to OX-B chain. These results indicate that derivatization of the cysteine thiols, through disulfide bonds, oxidation, or carboxyamidomethylation, radically affects T cell recognition of insulin B chain.

Requirements for simian immunodeficiency virus antigen-specific in vitro proliferation of T cells from infected rhesus macaques and sooty mangabeys

The measurement of cell-mediated immunity against the etiologic agent of human AIDS (HIV) in the non-human primate model of AIDS (simian immunodeficiency virus, SIV) has been difficult. In general, culture of peripheral blood mononuclear cells from HIV-1- and SIV-infected humans and monkeys, respectively, with purified inactivated HIV and SIV virus preparations has given inconsistent or negative proliferative responses. However, we describe herein an assay which consists of coculturing monocytes that have been pulsed with inactivated SIVsmm with nylon-wool-purified autologous T cells, leading to antigen-specific T-cell proliferation. The proliferative response, which predominantly occurs in CD4+ T cells, is major histocompatibility complex (MHC) class II-restricted and requires antigen processing. This assay will greatly facilitate the identification of the immunodominant epitopes recognized by T cells in sooty mangabeys, which are naturally infected but remain clinically asymptomatic, and in rhesus macaques, in which experimental infection leads to clinical symptomatology similar to human AIDS, eventually resulting in death.

Regulation of antigen presentation by acidic pH

The effect of pH on functional association of peptide antigens with APC membranes was investigated by using aldehyde-fixed B cells and class II-restricted T cell hybridomas to assess antigen/MHC complex formation. The results indicated that the rate and extent of functional peptide binding was markedly increased at pH 5.0 as compared with pH 7.3. The pH dependence of binding was preserved after pretreatment of fixed APC with pH 5.0 buffer, suggesting that pH had a direct effect on the interaction of peptide with the APC membrane. Similar results were obtained by using several peptides and I-Ad- and I-Ed-restricted T cells, indicating that pH may be of general importance in regulating the formation of functional antigen/class II MHC complexes.

Probing the structure of processed antigen by using biotin and avidin. MHC-dependent inhibition of responses to selected biotinyl-insulin derivatives

Current models suggest that Ag undergoes proteolytic cleavage in APC and that resultant peptide fragments associate with class II histocompatibility glycoproteins before recognition by helper T cells. Little direct information is available concerning the physical structure and membrane association of Ag processed under physiologic conditions. A model system, employing a series of biotinylated insulin derivatives, was used to examine the domains of Ag that are presented by APC. We reasoned that avidin should block the response of T cells to a given derivative only if biotin is retained on the functionally relevant form of Ag after processing. By utilizing derivatives modified at selected sites one should be able to determine whether specific sites remain after processing. By using F1 APC pulsed with biotinyl-insulin derivatives modified through the free amino groups of the A1, B1, or B29 amino acids, and T cell hybridomas restricted to I-Ad or I-Ab, we found that avidin inhibited the I-Ad-restricted response to A1, but not B1 or B29 derivatives. By contrast, specific inhibition of the I-Ab-restricted response was observed by using all three derivatives. These results suggest that the processed form of insulin recognized in association with I-Ab is largely intact and includes residues from both chains (A1, B1, and B29). The differential inhibition observed by using T cells restricted to different class II alleles demonstrates that processed Ag associated with I-Ab differs in conformation or structure from that associated with I-Ad. This experimental approach should prove valuable in characterizing the actual structure of processed Ag recognized by T cells.

Probing the structure of processed antigen by using biotin and avidin. MHC-dependent inhibition of responses to selected biotinyl-insulin derivatives

Current models suggest that Ag undergoes proteolytic cleavage in APC and that resultant peptide fragments associate with class II histocompatibility glycoproteins before recognition by helper T cells. Little direct information is available concerning the physical structure and membrane association of Ag processed under physiologic conditions. A model system, employing a series of biotinylated insulin derivatives, was used to examine the domains of Ag that are presented by APC. We reasoned that avidin should block the response of T cells to a given derivative only if biotin is retained on the functionally relevant form of Ag after processing. By utilizing derivatives modified at selected sites one should be able to determine whether specific sites remain after processing. By using F1 APC pulsed with biotinyl-insulin derivatives modified through the free amino groups of the A1, B1, or B29 amino acids, and T cell hybridomas restricted to I-Ad or I-Ab, we found that avidin inhibited the I-Ad-restricted response to A1, but not B1 or B29 derivatives. By contrast, specific inhibition of the I-Ab-restricted response was observed by using all three derivatives. These results suggest that the processed form of insulin recognized in association with I-Ab is largely intact and includes residues from both chains (A1, B1, and B29). The differential inhibition observed by using T cells restricted to different class II alleles demonstrates that processed Ag associated with I-Ab differs in conformation or structure from that associated with I-Ad. This experimental approach should prove valuable in characterizing the actual structure of processed Ag recognized by T cells.