Addressing Mental Health Barriers in HIV Care Coordination Is Crucial to Providing Optimal HIV/AIDS Care

For people with HIV (PWH) who have psychological comorbidities, effective management of mental health issues is crucial to achieving and maintaining viral suppression. Care coordination programs (CCPs) have been shown to improve outcomes across the HIV care continuum, but little research has focused on the role of care coordination in supporting the mental health of PWH. This study reports qualitative findings from the Program Refinements to Optimize Model Impact and Scalability based on Evidence (PROMISE) study, which evaluated a revised version of an HIV CCP for Ryan White Part A clients in New York City. Semistructured interviews were conducted with 30 providers and 27 clients from 6 CCP-implementing agencies to elucidate barriers and facilitators of program engagement. Transcripts were analyzed for key themes related to clients' mental health needs and providers' successes and challenges in meeting these needs. Providers and clients agreed that insufficiently managed mental health issues are a common barrier to achieving and maintaining viral suppression. Although the CCP model calls for providers to address clients' unmet mental health needs primarily through screening and referrals to psychiatric and/or psychological care, both clients and providers reported that the routine provision of emotional support is a major part of providers' role that is highly valued by clients. Some concerns raised by providers included insufficient training to address clients' mental health needs and an inability to document the provision of emotional support as a delivered service. These findings suggest the potential value of formally integrating mental health services into HIV care coordination provision. ClinicalTrials.gov protocol number: NCT03628287.

Client preferences for HIV Care Coordination Program features in New York City: latent class analysis of a discrete choice experiment

INTRODUCTION

The PROMISE study, launched in 2018, evaluates the implementation of revisions to the HIV Care Coordination Program (CCP) designed to minimize persistent disparities in HIV outcomes among high-need persons living with HIV in New York City. We conducted a discrete choice experiment (DCE) assessing the preferences of CCP clients to inform improvements to the program's design.

METHODS

Clients chose between two hypothetical CCP options that varied across four program attributes: help with antiretroviral therapy (ART) adherence (directly observed therapy [DOT] vs. remind via phone/text vs. adherence assessment), help with primary care appointments (remind and accompany vs. remind and transport vs. remind only), help with issues other than primary care (coverage and benefits vs. housing and food vs. mental health vs. specialty medical care) and visit location (meet at home vs. via phone/video vs. program visit 30 or 60 minutes away). The latent class analysis identified different preference patterns. A choice simulation was performed to model client preferences for hypothetical CCPs as a whole.

RESULTS

One hundred and eighty-one CCP clients from six sites implementing the revised CCP completed the DCE January 2020-March 2021. Most clients had stable housing (68.5%), reported no problem substance use in the last 3 months (72.4%) and achieved viral suppression (78.5) with only 26.5% receiving DOT within a CCP. 77.3% of responses were obtained before the COVID-19 pandemic. Preferences clustered into three groups. Visit location and ART adherence support were the most important attributes. Group 1 (40%) endorsed telehealth for visit location; telehealth for ART adherence support; and help with securing housing/food; Group 2 (37%) endorsed telehealth for visit location; telehealth for ART adherence support; and staff reminding/arranging appointment transportation; Group 3 (23%) endorsed staff meeting clients at program location and staff working with clients for medication adherence. In the choice simulation, Basic and Medium hypothetical CCPs were endorsed more than Intensive CCPs.

CONCLUSIONS

This DCE revealed a strong preference for telehealth and a relatively low preference for intensive services, such as DOT and home visits; preferences were heterogeneous. The findings support differentiated care and remote service delivery options in the NYC CCP, and can inform improvements to CCP design.

High-Sensitivity Dry Rehydratable Film Method for Enumeration of Coliforms in Dairy Products: Collaborative Study

A dry-film coliform count plate that is inoculated with 5 mL sample was compared with the Violet Red Bile Agar plate method in a collaborative study by 18 laboratories. Products analyzed were 2% milk, chocolate milk, cream, vanilla ice cream, cottage cheese, and cheese. Collaborators tested blind duplicate uninoculated samples and samples inoculated at low, medium, and high level. Significantly (P< 0.05) higher numbers of coliforms were recovered by the dry-film method from 2% milk samples at the 3 inoculum levels, the chocolate milk at the low- and high-inoculum levels, and the cream at the high-inoculum level. Significantly higher counts were obtained by the agar method for cottage cheese samples at the low-inoculum level. The repeatability standard deviation for the dry-film method was significantly higher for the high-inoculum level chocolate milk sample and the medium-inoculum level cottage cheese. The same statistic was significantly higher for the agar method at all 3 inoculum levels in the 2% milk and the medium-inoculum level cream. The high-sensitivity dry rehydratable film method for enumeration of coliforms in dairy products has been adopted first action by AOAC INTERNATIONAL.

Successful isolated intestinal transplantation in sensitized recipients with the use of virtual crossmatching

We evaluated virtual crossmatching (VXM) for organ allocation and immunologic risk reduction in sensitized isolated intestinal transplantation recipients. All isolated intestine transplants performed at our institution from 2008 to 2011 were included in this study. Allograft allocation in sensitized recipients was based on the results of a VXM, in which the donor-specific antibody (DSA) was prospectively evaluated with the use of single-antigen assays. A total of 42 isolated intestine transplants (13 pediatric and 29 adult) were performed during this time period, with a median follow-up of 20 months (6-40 months). A sensitized (PRA ≥ 20%) group (n = 15) was compared to a control (PRA < 20%) group (n = 27) to evaluate the efficacy of VXM. With the use of VXM, 80% (12/15) of the sensitized patients were transplanted with a negative or weakly positive flow-cytometry crossmatch and 86.7% (13/15) with zero or only low-titer (≤ 1:16) DSA. Outcomes were comparable between sensitized and control recipients, including 1-year freedom from rejection (53.3% and 66.7% respectively, p = 0.367), 1-year patient survival (73.3% and 88.9% respectively, p = 0.197) and 1-year graft survival (66.7% and 85.2% respectively, p = 0.167). In conclusion, a VXM strategy to optimize organ allocation enables sensitized patients to successfully undergo isolated intestinal transplantation with acceptable short-term outcomes.

Adrenalectomy blocks the compensatory increases in UT-A1 and AQP2 in diabetic rat kidney

In normal rats we showed that glucocorticoids participate in the downregulation of UT-A1 protein abundance in the inner medullary tip and in lowering of basal and vasopressin-stimulated facilitated urea permeability in terminal IMCDs. To examine the relevance of this response to a rat model of human disease, we studied rats with uncontrolled diabetes mellitus (DM) induced by streptozotocin (STZ), since these rats have increased corticosterone production and urea excretion. We found that at 3 days of DM, UT-A1 protein abundance is downregulated in the inner medullary tip compared to pair-fed control rats, while DM for more than 7 days caused an increase in UT-A1. To test whether adrenal steroids could be a mechanism contributing to the latter increase, we studied adrenalectomized rats (ADX), ADX rats given STZ to induce diabetes (ADX + STZ), and ADX + STZ rats receiving exogenous aldosterone or dexamethasone. In contrast to control rats, UT-A1 protein abundance was not increased by prolonged DM in the ADX rats. Aquaporin 2 (AQP2) was not increased in the inner medullas of 10-day DM rats either. However, UT-A1 protein abundance was significantly reduced in the inner medullary tips from both diabetic aldosterone-treated (40 +/- 2%) and dexamethasone-treated (43 +/- 2%) ADX rats compared to diabetic ADX rats without steroid replacement. AQP2 was unaffected by steroid hormone treatments. Thus, both mineralocorticoids and glucocorticoids downregulate UT-A1 protein abundance in rats with uncontrolled diabetes mellitus for 10 days. These results suggest that: 1) the increase in UT-A1 observed in DM is dependent upon having adrenal steroids present; and 2) adrenal steroids are not sufficient to enable the compensatory rise in UT-A1 to a steroid-deficient diabetic animal.

Kinetics and thermodynamics of beta 2-microglobulin binding to the alpha 3 domain of major histocompatibility complex class I heavy chain

The major histocompatibility complex (MHC) class I molecule plays a crucial role in cytotoxic lymphocyte function. Functional class I MHC exists as a heterotrimer consisting of the MHC class I heavy chain, an antigenic peptide fragment, and beta2-microglobulin (beta2m). beta2m has been previously shown to play an important role in the folding of the MHC heavy chain without continued beta2m association with the MHC complex. Therefore, beta2m is both a structural component of the MHC complex and a chaperone-like molecule for MHC folding. In this study we provide data supporting a model in which the chaperone-like role of beta2m is dependent on initial binding to only one of the two beta2m interfaces with class 1 heavy chain. beta2-Microglobulin binding to an isolated alpha3 domain of the class I MHC heavy chain accurately models the biochemistry and thermodynamics of beta2m-driven refolding. Our results explain a 1000-fold discrepancy between beta2m binding and refolding of MHC1. The biochemical study of the individual domains of complex molecules is an important strategy for understanding their dynamic structure and multiple functions.

ICAM-1 enhances MHC-peptide activation of CD8(+) T cells without an organized immunological synapse

In addition to the TCR-ligand interaction, other receptor-ligand pairs, such as LFA-1 and ICAM-1, play a major role in the activation of T cells. Recent studies of T cell activation suggest a coordinated movement of LFA-1 and ICAM-1 in forming a defined zone in the immunological synapse. It is unclear from these studies whether the organized molecular geometry of the immunological synapse is necessary for ICAM-1 enhancement of T cell activation. In this report, we demonstrate that ICAM-1 can enhance the activation of CD8(+) T cells by MHC-peptide in the absence of an organized immunologic synapse. Therefore, although the molecular organization of the immunologic synapse may amplify stimuli, it is not an absolute requirement for either CD8(+) T cell activation or the ICAM-1 enhancement of TCR activation.

Mucin inhibition of lymphocyte function does not require specific mucin-ligand interactions

Mucins are large highly glycosylated molecules that have been postulated to interfere with certain cell-cell interactions. Steric, charge and specific signalling effects have been postulated for the inhibition by cell-surface mucin molecules. In this report we evaluate the inhibitory effects of bovine submaxillary mucin (BSM), a mucin without specific lymphocyte interactions, on lymphocyte function. BSM inhibits the adhesion of lymphocytes when coimmobilized with intercellular adhesion molecule-1 (ICAM-1) and blocks the activation of T lymphocytes when coimmobilized with anti-CD3. These data demonstrate a general mucin effect on lymphocyte adhesion and activation that is primarily steric in nature and implicates mucins as general barriers to lymphocyte-tumour cell interactions. Mucin blockade of cell-cell interactions may explain why mucinous tumours are often associated with a poor prognosis.

The isolated major histocompatibility complex class I alpha3 domain binds beta2m and CD8alphaalpha dimers

The MHC class I molecule plays a crucial role in cytotoxic lymphocyte function. The heavy chain of the MHC class I molecule can form many non-covalent interactions with other molecules on multiple domains and surfaces. We have generated an isolated alpha3 domain of a murine MHC class I molecule and evaluated the contribution of this domain to binding with the MHC class I light chain, beta2m, and CD8. The alpha3 domain binds beta2m at a thousand-fold higher concentration than the whole MHC, and binds CD8alphaalpha with a dependence on the alpha3 CD loop. Our results are relevant for models of MHC folding and CD8-MHC function. The study of individual domains of complex molecules is an important strategy for understanding their dynamic structure and function.

ICAM-1 co-stimulation has differential effects on the activation of CD4+ and CD8+ T cells

T cells play a central role in the initiation, maintenance and regulation of the immune response. Effector responses of T cells are controlled by complex combinations of lymphokines and adhesion/co-stimulatory molecule signals. To isolate the effects of the adhesion/co-stimulatory molecule ICAM-1, we have stimulated purified murine CD4+ and CD8+ T cells with plate-bound anti-CD3 in the presence or absence of plate-bound soluble ICAM-1. In this report, we demonstrate that the co-immobilization of soluble ICAM-1 and anti-CD3 leads to a much greater increase in IL-2 production by CD8+ T cells than CD4+ T cells. The ICAM-1-induced enhancement we observed has differential sensitivity to LFA-1 blockade, depending on the T cell subsets and cytokine evaluated. These effects may play an important role in the generation and modulation of immune responses.

Purified MHC class I and peptide complexes activate naive CD8+ T cells independently of the CD28/B7 and LFA-1/ICAM-1 costimulatory interactions

T cells play a central role in the initiation, maintenance, and regulation of the immune response. Effector responses of T cells are controlled by complex combinations of lymphokines and adhesion/costimulatory molecule signals. To isolate the effects of specific adhesion/costimulatory molecules and to define the minimal molecular requirements of naive CD8+ T cell activation, we have developed an APC-free system for stimulation of naive CD8+ T cells. In this report, we demonstrate that immobilized MHC class I-peptide complexes can activate naive CD8+ T cells from TCR transgenic mice at low cell densities. The CD8+ T cells were stimulated to proliferate and secrete IL-2 independently of the molecular interactions between CD28/B7.1-B7.2 or LFA-1/ICAM-1 surface receptors. Previous reports have shown that CD28 ligation is necessary for late T cell survival of APC-stimulated naive CD8+ T cells. Our data suggest that under certain specific conditions of high intensity T cell signaling, early activation and late cell proliferation can occur independently of APC-derived costimulatory signals.

Degenerate MHC restriction reveals the contribution of class I MHC molecules in determining the fine specificity of CTL recognition of an immunodominant determinant of HIV-1 gp160 V3 loop

The novel allogeneic presentation of an immunodominant determinant within the HIV-1 gp160 V3 loop by three different class I MHC molecules to the same CD8+ CTL is used to study the influence of the MHC molecule on the fine specificity of CTL recognition. We previously reported that four distinct class I molecules of H-2d,u,p,q presented the V3 decapeptide P18-I10 (RGPGRAFVTI) to CTL. Surprisingly, we found that H-2d,u,p cells mutually cross-present the P18-I10 peptide to allogeneic CTL clones of each of the other haplotypes, whereas none of these cross-presents to H-2q CTL, nor do H-2q targets present to CTL of the other haplotypes. Here, we explore the critical amino acid residues for the cross-presentation using 10 variant peptides with single amino acid substitutions. The fine specificity examined using these mutant peptides presented by the same MHC class I molecule showed striking similarity among the CTL of each haplotype, expressing either V beta 8.1 or V beta 14. In contrast, the fine specificity is different between the distinct MHC class I molecules even for the lysis by the same CTL, as shown by reciprocal effects of the same substitutions. Thus, peptide fine specificity of a single TCR is influenced by changes in the class I MHC molecules presenting the Ag.

Naive alloreactive CD8 T cells are activated by purified major histocompatibility complex class I and antigenic peptide

In this report, we demonstrate stimulation of T cell receptor (TCR) transgenic CD8 T cells by isolated major histocompatibility complex (MHC) class I H-2Ld complexes and antigenic peptide. This is the first demonstration of CD8 T cells activated by MHC and antigenic peptide in the absence of antigen priming. Furthermore, isolated MHC and a potent peptide antigen can stimulate phenotypically naive CD44- T cells to become CTL effectors and to produce interleukin-2 in nanogram per milliliter amounts. These results demonstrate that particular TCR antigen pairs may overcome the need for specialized antigen-presenting cells and have implications for mechanisms of autoimmunity and tolerance induction.

Degenerate MHC restriction reveals the contribution of class I MHC molecules in determining the fine specificity of CTL recognition of an immunodominant determinant of HIV-1 gp160 V3 loop

The novel allogeneic presentation of an immunodominant determinant within the HIV-1 gp160 V3 loop by three different class I MHC molecules to the same CD8+ CTL is used to study the influence of the MHC molecule on the fine specificity of CTL recognition. We previously reported that four distinct class I molecules of H-2d,u,p,q presented the V3 decapeptide P18-I10 (RGPGRAFVTI) to CTL. Surprisingly, we found that H-2d,u,p cells mutually cross-present the P18-I10 peptide to allogeneic CTL clones of each of the other haplotypes, whereas none of these cross-presents to H-2q CTL, nor do H-2q targets present to CTL of the other haplotypes. Here, we explore the critical amino acid residues for the cross-presentation using 10 variant peptides with single amino acid substitutions. The fine specificity examined using these mutant peptides presented by the same MHC class I molecule showed striking similarity among the CTL of each haplotype, expressing either V beta 8.1 or V beta 14. In contrast, the fine specificity is different between the distinct MHC class I molecules even for the lysis by the same CTL, as shown by reciprocal effects of the same substitutions. Thus, peptide fine specificity of a single TCR is influenced by changes in the class I MHC molecules presenting the Ag.

CD27-CD70 interactions regulate B-cell activation by T cells

CD27, a member of the tumor necrosis factor (TNF) receptor family, binds to its ligand CD70, a member of the TNF family, and subsequently induces T-cell costimulation and B-cell activation. CD27 is expressed on resting T and B cells, whereas CD70 is expressed on activated T and B cells. Utilizing transfected murine pre-B-cell lines expressing human CD27 or CD70, we have examined the effect of such transfectant cells on human B-cell IgG production and B-cell proliferation. We show that the addition of CD27-transfected cells to a T-cell-dependent, pokeweed mitogen-driven B-cell IgG synthesis system resulted in marked inhibition of IgG production, whereas the addition of CD70-transfected cells enhanced IgG production. The inhibition and enhancement of pokeweed mitogen-driven IgG production by CD27 and CD70 transfectants were abrogated by pretreatment with anti-CD27 and anti-CD70 monoclonal antibodies, respectively. In contrast, little or no inhibition of IgG production and B-cell proliferation was noted with CD27-transfected cells or either anti-CD27 or CD70 monoclonal antibody in a T-cell-independent Staphylococcus aureus/interleukin 2-driven B-cell activation system. In this same system CD70-transfected cells enhanced B-cell IgG production and B-cell proliferation, and this enhancement could be gradually abrogated by addition of increasing numbers of CD27-transfected cells. These results clearly demonstrate that interactions among subsets of T cells expressing CD27 and CD70 play a key role in regulating B-cell activation and immunoglobulin synthesis.

Molecular analysis of the same HIV peptide functionally binding to both a class I and a class II MHC molecule

Although several peptides have been found to bind to both class I and class II molecules, the basis for this binding of the same peptide to two classes of MHC molecules has not been compared previously. We have analyzed one such peptide, P18 from the V3 loop of HIV-1 gp160, which we have previously shown to be recognized by CD8+ CTL with the class I molecule H-2Dd, and by CD4+ Th cells with the class II molecule I-Ad. With the use of truncated and substituted peptides, we found that the minimal core peptides are very similar, that the residues required for class I binding precisely fit the recently identified consensus motif for peptides binding to Dd (XGPX[R/K/H]XXX(X) [L/I/F]), and that at least three of the same residues are involved in binding to class II I-Ad. In addition, several of the same residues are involved in TCR interaction when the peptide is presented by class I and class II molecules. Modeling shows results to be consistent with the crystal structure of a peptide-class II MHC complex. Thus, the recognition of this versatile peptide by CD4+ Th cells with class II MHC molecules and by CD8+ cytotoxic T cells with class I MHC molecules is remarkably similar in both the core peptide used and the role of different residues in the ternary complex.

Molecular analysis of the same HIV peptide functionally binding to both a class I and a class II MHC molecule

Although several peptides have been found to bind to both class I and class II molecules, the basis for this binding of the same peptide to two classes of MHC molecules has not been compared previously. We have analyzed one such peptide, P18 from the V3 loop of HIV-1 gp160, which we have previously shown to be recognized by CD8+ CTL with the class I molecule H-2Dd, and by CD4+ Th cells with the class II molecule I-Ad. With the use of truncated and substituted peptides, we found that the minimal core peptides are very similar, that the residues required for class I binding precisely fit the recently identified consensus motif for peptides binding to Dd (XGPX[R/K/H]XXX(X) [L/I/F]), and that at least three of the same residues are involved in binding to class II I-Ad. In addition, several of the same residues are involved in TCR interaction when the peptide is presented by class I and class II molecules. Modeling shows results to be consistent with the crystal structure of a peptide-class II MHC complex. Thus, the recognition of this versatile peptide by CD4+ Th cells with class II MHC molecules and by CD8+ cytotoxic T cells with class I MHC molecules is remarkably similar in both the core peptide used and the role of different residues in the ternary complex.

Minimal requirements for peptide mediated activation of CD8+ CTL

A physical chemical model of T cell stimulation by class I-peptide complexes was developed and used to analyse in vitro studies of gamma-interferon release as a function of the number of peptide and MHC molecules. The analysis provided reasonable estimates of well identified parameters, including equilibrium constants and the minimum number of T cell receptor-class I-peptide ternary complexes on a presenting cell required to activate T cells. The latter number was estimated as 3-5 per T cell. This is in distinct contrast to estimates in the literature of the number of peptide-MHC complexes required for activity, which is necessarily larger. The analysis also predicted that activity is potentiated by interaction between class I molecules, even if one member of the pair is not bound by antigen. The analytical approach used in this paper may be applicable to other activation systems.

Functional cell surface expression by a recombinant single-chain class I major histocompatibility complex molecule with a cis-active beta 2-microglobulin domain

As a preliminary step towards the use of cell surface single-chain class I major histocompatibility complex (MHC) molecules as T cell immunogens, we have engineered a recombinant gene encoding a full-length cell surface single-chain version of the H-2Dd class I MHC molecule (SC beta Ddm) which has beta 2-microglobulin (beta 2m) covalently linked to the amino terminus of a full-length H-2Dd heavy chain via a peptide spacer. The single-chain protein is correctly folded and stably expressed on the surface of transfected L cells. It can present an antigenic peptide to an H-2Dd-restricted antigen-specific T cell hybridoma. When expressed in peptide-transport-deficient cells, SC beta Ddm can be stabilized and pulsed for antigen presentation by incubation with extracellular peptide at 27 degrees or 37 degrees C, allowing the preparation of cells with single-chain molecules that are loaded with a single chosen antigenic peptide. SC beta Ddm can be stably expressed in beta 2m-negative cells, showing that the single-chain molecule uses its own beta 2m domain to achieve correct folding and surface expression. Furthermore, the beta 2m domain of SC beta Ddm, unlike transfected free beta 2m, does not rescue surface expression of endogenous class I MHC in the beta 2m-negative cells. This strict cis activity of the beta 2m domain of SC beta Ddm makes possible the investigation of class I MHC function in cells, and potentially in animals, that express but a single type of class I MHC molecule.

Multiple pathways are involved in the extracellular processing of MHC class I-restricted peptides

T cell stimulation by certain class I-restricted antigenic peptides, such as the HIV 1 gp160-derived peptide, P18, requires peptide processing by angiotensin-1 converting enzyme (ACE) in FCS. We observed that longer versions of P18 and the murine cytomegalovirus pp89-derived core peptide, pMCMV, which could stimulate T cell hybridomas in FCS, were not as sensitive to the ACE inhibitor captopril as P18. Using cell-free soluble murine class I MHC molecules and protease inhibitors, we found that there are pathways of differing efficiency that use enzymes other than ACE for the proteolytic processing of peptides in serum. The kinetics of the generation of T cell stimulatory activity among P18 variant peptides in serum differed with peptide length, and with the nature of amino and COOH-terminal extensions. Such processing occurs in human plasma as well as in FCS. The understanding of this processing, its kinetics, and its inhibitors can lead to better design of peptide-based therapies, including vaccines.

Multiple pathways are involved in the extracellular processing of MHC class I-restricted peptides

T cell stimulation by certain class I-restricted antigenic peptides, such as the HIV 1 gp160-derived peptide, P18, requires peptide processing by angiotensin-1 converting enzyme (ACE) in FCS. We observed that longer versions of P18 and the murine cytomegalovirus pp89-derived core peptide, pMCMV, which could stimulate T cell hybridomas in FCS, were not as sensitive to the ACE inhibitor captopril as P18. Using cell-free soluble murine class I MHC molecules and protease inhibitors, we found that there are pathways of differing efficiency that use enzymes other than ACE for the proteolytic processing of peptides in serum. The kinetics of the generation of T cell stimulatory activity among P18 variant peptides in serum differed with peptide length, and with the nature of amino and COOH-terminal extensions. Such processing occurs in human plasma as well as in FCS. The understanding of this processing, its kinetics, and its inhibitors can lead to better design of peptide-based therapies, including vaccines.

Role of conserved regions of class I MHC molecules in the activation of CD8+ cytotoxic T lymphocytes by peptide and purified cell-free class I molecules

To analyze the molecular interactions involved in CD8+ cytotoxic T lymphocyte (CTL) recognition quantitatively, we developed a cell-free antigen presenting system. Genetically engineered soluble H-2Dd molecules coated on plastic microtiter plates could present HIV envelope peptide to an antigen-specific CTL clone, inducing it to produce IFN-gamma in the absence of accessory cells and their accessory or co-stimulatory molecules. The peptide-MHC complexes were functionally stable for over 24 h. The magnitude of T cell activation was dependent on the concentrations of both class I MHC molecule and the peptide, but was more sensitive to the concentration of the MHC molecule than to that of peptide. This result suggests that one MHC molecule can play more than one role in activating the CTL. One such role is the interaction between CD8 and a conserved region of class I MHC, as suggested by the finding that holding the total MHC concentration constant with an irrelevant class I MHC molecule (H-2Kb engineered to have the same alpha 3 domain as H-2Dd) made the T cell response less sensitive to the change in concentration of the relevant MHC molecule (H-2Dd). The irrelevant class I MHC molecule (H-2Kb), unable to present this peptide by itself, augmented the T cell response at lower concentrations of peptide. These results suggest that the conserved alpha 3 domain of the class I MHC heavy chain as well as polymorphic regions play an important role in T cell activation and that T cell interaction with MHC molecules not presenting peptide can still augment the response.

A soluble divalent class I major histocompatibility complex molecule inhibits alloreactive T cells at nanomolar concentrations

Genetically engineered or chemically purified soluble monovalent major histocompatibility complex (MHC) molecules, which have previously been used to study T cells, have not blocked cytotoxic T-cell responses. Here we describe a genetically engineered divalent class I MHC molecule which inhibits lysis of target cells by alloreactive cytotoxic T cells. This protein, H-2Kb/IgG, was generated as a fusion protein between the extracellular domains of a murine class I polypeptide, H-2Kb, and an immunoglobulin heavy chain polypeptide. The chimeric protein has serological and biochemical characteristics of both the MHC and IgG polypeptides. Nanomolar concentrations of H-2Kb/IgG inhibited lysis of H-2Kb-expressing target cells not only by alloreactive H-2Kb-specific T-cell clones but also by alloreactive H-2Kb-specific primary T-cell cultures. A direct binding assay showed high-affinity binding between the H-2Kb/IgG molecule and an H-2Kb-specific alloreactive T-cell clone. Unlabeled H-2Kb/IgG displaced 125I-labeled H-2Kb/IgG from T cells with an IC50 of 1.2 nM.

Endogenous peptides of a soluble major histocompatibility complex class I molecule, H-2Lds: sequence motif, quantitative binding, and molecular modeling of the complex

To gain insight into the rules that govern the binding of endogenous and viral peptides to a given major histocompatibility complex (MHC) class I molecule, we characterized the amino acid sequences of a set of self peptides bound by a soluble analogue of murine H-2Ld, H-2Lds. We tested corresponding synthetic peptides quantitatively for binding in several different assays, and built three-dimensional computer models of eight peptide/H-2Lds complexes, based on the crystallographic structure of the human HLA-B27/peptide complex. Comparison of primary and tertiary structures of bound self and antigenic peptides revealed that residues 2 and 9 were not only restricted in sequence and tolerant of conservative substitutions, but were spatially constrained in the three-dimensional models. The degree of sequence variability of specific residues in MHC-restricted peptides reflected the lack of structural constraint on those amino acids. Thus, amino acid residues that define a peptide motif represent side chains required or preferred for a close fit with the MHC class I heavy chain.

A recombinant, soluble, single-chain class I major histocompatibility complex molecule with biological activity

Heterodimeric class I major histocompatibility complex molecules, which consist of a 45-kDa heavy-chain and a 12-kDa beta 2-microglobulin (beta 2m) light chain, bind endogenously synthesized peptides for presentation to antigen-specific T cells. We have synthesized a gene encoding a single-chain, soluble class I molecule derived from mouse H-2Dd, in which the carboxyl terminus of beta 2m is linked via a peptide spacer to the amino terminus of the heavy chain. The chimeric protein is secreted efficiently from transfected L cells, is thermostable, and when loaded with an appropriate antigenic peptide, stimulates an H-2Dd-restricted antigen-specific T-cell hybridoma. Thus, functional binding of peptide does not require the complete dissociation of beta 2m, implying that a heavy chain/peptide complex is not an obligate intermediate in the assembly of the heavy-chain/beta 2m/peptide heterotrimer. Single-chain major histocompatibility complex molecules uniformly loaded with peptide have potential uses for structural studies, toxin or fluor conjugates, and vaccines.

Exercise performance, core temperature, and metabolism after prolonged restricted activity and retraining in dogs

To study physiological effects of restricted activity (RA) and subsequent retraining, 10 male mongrel dogs (1-5 years) performed a submaximal exercise endurance test on a treadmill (12 degrees slope, 1.6 m.s-1) during kennel control, after 8 weeks of cage (40 cm-w x 80 cm-h x 110 cm-l) confinement, and after 8 weeks of retraining using the same treadmill protocol 1 h/d for 6 d/week. Compared with control endurance (172 +/- 19 min), endurance decreased to 102 +/- 15 min (delta = -41%, p less than 0.05) after RA and increased to 223 +/- 24 min (delta = +30%, p less than 0.05) after training: the respective final levels and changes in rectal temperature were 41.25 and +2.15 degrees C, 41.60 and +2.70 degrees C (NS), and 41.35 and +2.40 degrees C (NS), respectively. Resting and post-exercise blood glucose and lactate concentrations were unchanged in the three experiments. After RA, resting muscle glycogen was reduced from a control level of 49.9 +/- 4.3 to 34.1 +/- 4.5 mmol.kg-1 (delta = 32%, p less than 0.05) which returned to the control level of 58.4 +/- 3.5 mmol.kg-1 after retraining. Resting plasma FFA levels were unchanged, but the RA post-exercise change was decreased from a control level of +0.400 +/- 0.099 to +0.226 +/- 0.039 mmol.L-1 (p less than 0.05). Neither restricted activity nor training affected glucose tolerance significantly. The results indicated that RA reduces exercise endurance, the effectiveness of exercise thermoregulation, muscle glycogen stores, and the lipolytic response to exercise and to noradrenaline stimulation. All these changes were reversed following 8 weeks of retraining.

Peptide and beta 2-microglobulin regulation of cell surface MHC class I conformation and expression

We have examined the roles of peptide and beta 2-microglobulin (beta 2m) in regulating the conformation and expression level of class I molecules on the cell surface. Using a cell line synthesizing H-2Dd H chain and mouse beta 2m but defective in endogenous peptide loading, we demonstrate the ability of either exogenous peptide or beta 2m alone to increase surface H-2Dd expression at both 25 degrees C and 37 degrees C. Peptide and beta 2m show marked synergy in their abilities to increase surface class I expression, with minimal increases promoted by peptide in the absence of free beta 2m. Low temperature-induced molecules have indistinguishable rates of loss of beta 2m and alpha 1/alpha 2 domain conformational epitopes during culture at 37 degrees C. However, the rate of alpha 3 epitope loss is much slower, indicating a minimum of two steps in class I loss from the cell surface: 1) loss of beta 2m binding to H chain and unfolding of the alpha 1/alpha 2 region; then 2) denaturation, degradation, or internalization of the free H chains possessing alpha 3 epitopes. These data show for the first time that free H chains survive for a finite time on the membrane in a form capable of refolding into alpha 1/alpha 2 epitope positive molecules upon addition of beta 2m and peptide. This refolding in the presence of beta 2m and peptide can explain the reported requirement for both components in sensitizing cells for class I-dependent CTL lysis. It also indicates that such conformational changes in class I molecules are not strictly dependent on either newly synthesized H chains or on intracellular chaperons. The study of H chain-peptide-beta 2m interaction on the cell surface may be relevant to understanding intracellular peptide loading events.

Peptide and beta 2-microglobulin regulation of cell surface MHC class I conformation and expression

We have examined the roles of peptide and beta 2-microglobulin (beta 2m) in regulating the conformation and expression level of class I molecules on the cell surface. Using a cell line synthesizing H-2Dd H chain and mouse beta 2m but defective in endogenous peptide loading, we demonstrate the ability of either exogenous peptide or beta 2m alone to increase surface H-2Dd expression at both 25 degrees C and 37 degrees C. Peptide and beta 2m show marked synergy in their abilities to increase surface class I expression, with minimal increases promoted by peptide in the absence of free beta 2m. Low temperature-induced molecules have indistinguishable rates of loss of beta 2m and alpha 1/alpha 2 domain conformational epitopes during culture at 37 degrees C. However, the rate of alpha 3 epitope loss is much slower, indicating a minimum of two steps in class I loss from the cell surface: 1) loss of beta 2m binding to H chain and unfolding of the alpha 1/alpha 2 region; then 2) denaturation, degradation, or internalization of the free H chains possessing alpha 3 epitopes. These data show for the first time that free H chains survive for a finite time on the membrane in a form capable of refolding into alpha 1/alpha 2 epitope positive molecules upon addition of beta 2m and peptide. This refolding in the presence of beta 2m and peptide can explain the reported requirement for both components in sensitizing cells for class I-dependent CTL lysis. It also indicates that such conformational changes in class I molecules are not strictly dependent on either newly synthesized H chains or on intracellular chaperons. The study of H chain-peptide-beta 2m interaction on the cell surface may be relevant to understanding intracellular peptide loading events.

Serum angiotensin-1 converting enzyme activity processes a human immunodeficiency virus 1 gp160 peptide for presentation by major histocompatibility complex class I molecules

T cell stimulation by the human immunodeficiency virus 1 gp160-derived peptide p18 presented by H-2Dd class I major histocompatibility complex molecules in a cell-free system was found to require proteolytic cleavage. This extracellular processing was mediated by peptidases present in fetal calf serum. In vitro processing of p18 resulted in a distinct reverse phase high performance liquid chromatography profile, from which a biologically active product was isolated and sequenced. This peptide processing can be specifically blocked by the angiotensin-1 converting enzyme (ACE) inhibitor captopril, and can occur by exposing p18 to purified ACE. The ability of naturally occurring extracellular proteases to convert inactive peptides to T cell antigens has important implications for understanding cytotoxic T lymphocyte responses in vivo, and for rational peptide vaccine design.

Solution binding of an antigenic peptide to a major histocompatibility complex class I molecule and the role of beta 2-microglobulin

The major histocompatibility complex-encoded class I molecule, a noncovalent dimer of a polymorphic 45-kDa heavy chain and a nonpolymorphic 12-kDa beta 2-microglobulin (beta 2m) light chain, binds peptide antigen prior to its interaction with T-cell antigen receptors. We report here that the binding in aqueous solution at 37 degrees C of a soluble purified murine major histocompatibility complex class I protein, H-2Lds (a soluble analogue of H-2Ld consisting of the alpha 1 and alpha 2 domains of H-2Ld, the alpha 3 domain and the C terminus of Q10b), to an antigenic peptide is controlled by the light-chain subunit beta 2m. Analysis of the equilibrium binding data favors a model in which two classes of peptide binding sites exist, the high-affinity class having an equilibrium constant for dissociation, KH, of 3.7 x 10(-7) M and accounting for 12% of the theoretically available sites. Studies of binding in the presence of excess beta 2m indicate that this increases the concentration of available high-affinity sites. These data are consistent with a ternary model in which high-affinity sites are generated by the interaction of beta 2m with the peptide-binding class I heavy chain.

Abnormal growth patterns in diabetes in pregnancy: a longitudinal study

In this longitudinal study we sought to investigate the presence of different abnormal fetal growth patterns in the pregnant diabetic. At least three serial ultrasound examinations were performed during the third trimester on 522 diabetic and 93 control subjects. Growth curves were established for femur length, abdominal circumference and head circumference. In addition, daily growth rate was calculated for fetal weight and all morphometric measurements. The study revealed: a) in the gestational diabetes group large-for-gestational age infants, two accelerated growth patterns (early mean blood glucose 107 +/- 16 and late mean blood glucose 116 +/- 18) were identified; b) there was a significantly larger abdominal circumference (expressed as an age-related percentile) in the early than in the late pattern (88 +/- 10 vs. 60 +/- 18, P less than 0.05); c) femur length, head circumference and growth rate were similar for large-for-gestational age and appropriate-for-gestational age fetuses; d) in the control macrosomic infants (n = 57), the percentile of femur length, head circumference and abdominal circumference within 4 days of delivery were 91 +/- 11, 89 +/- 10, 60 +/- 26, respectively; e) analysis for small-for-gestational age infants showed a similarity in the morphometric measurements and growth rate of insulin-dependent diabetes mellitus and hypertensive control subjects; and f) in contrast, a significantly larger abdominal circumference was found in the gestational diabetes small-for-gestational age infants than in the previous small-for-gestational age groups. Recognition of the specific dynamics and characteristics of these patterns will allow for early detection of the fetus at risk, which in turn will improve clinical decision-making.

Excess beta 2 microglobulin promoting functional peptide association with purified soluble class I MHC molecules

T lymphocytes expressing alpha beta receptors recognize antigenic peptide fragments bound to major histocompatibility complex class I or class II molecules present on the surface membranes of other cells. Peptide fragments are present in the two available HLA crystal structures and recent data indicate that peptide is required for the stable folding of the class I heavy chain and maintenance of its association with the class I light chain, beta 2-microglobulin (beta 2m), at physiological temperature. To explain how the exogenous peptide used to create targets for cytotoxic cells bearing CD8 antigen could associate with apparently peptide-filled extracellular class I molecules, we hypothesized that stable binding of exogenous peptide to mature class I molecules reflects either the replacement of previously bound peptide during the well documented beta 2m exchange process or the loading of 'empty' class I heavy chains dependent on the availability of excess beta 2m. In either case, free beta 2m should enhance peptide/class I binding. Using either isolated soluble class I molecules or living cells, we show here that free purified beta 2m markedly augments the generation of antigenic complexes capable of T-cell stimulation.

Peritonitis due to Kluyvera ascorbata: case report and review

Kluyvera, a new genus in the family Enterobacteriaceae, was formerly known as enteric group 8 and as API group 1. Although Kluyvera species have been isolated from various clinical specimens such as sputum, urine, stool, and blood, the clinical significance of these isolates has not been established. Recently, we treated a child who developed peritonitis due to Kluyvera ascorbata. The repeated isolation of the organism in pure culture from the peritoneal fluid and its isolation from postmortem subdiaphragmatic microabscesses suggest that Kluyvera can be clinically significant. Review of the literature clearly indicates that Kluyvera strains are infrequent but potentially dangerous pathogens in humans. Further experience is needed to determine the therapeutic efficacy of the various antibiotics to which these bacteria are sensitive in vitro.

Effect of endurance training on cardiovascular response to static exercise performed with untrained muscles

Eighteen male volunteers (20-23 years) were submitted to 13 weeks of training consisting of 30 min of exercise (at 50%-75% VO2max) on a bicycle ergometer, performed three times a week. Every 4 weeks the heart rate (HR), blood pressure (BP), and systolic time interval (STI) responses to the static handgrip (at 30% MVC) were examined. Before and after 13 weeks of training echocardiograms were recorded in seven subjects at rest and during the handgrip. Significant decreases in HR and BP responses to static exercise were found already after 4 weeks of training. Resting STI and left ventricular dimensions were not affected by training, but during the static exercise the pre-ejection period (PEP) and isovolumic contraction time interval (ICT) at the corresponding HR were significantly shortened after 8 weeks of training. The values of echocardiographic indices of left ventricular function obtained during exercise after training did not differ significantly from those found before training. It is concluded that endurance training of moderate intensity improves cardiac function during static exercise performed with untrained muscles.

Plasma testosterone and catecholamine responses to physical exercise of different intensities in men

Plasma testosterone, noradrenaline, and adrenaline concentrations during three bicycle ergometer tests of the same total work output (2160 J X kg-1) but different intensity and duration were measured in healthy male subjects. Tests A and B consisted of three consecutive exercise bouts, lasting 6 min each, of either increasing (1.5, 2.0, 2.5 W X kg-1) or constant (2.0, 2.0, 2.0 W X kg-1) work loads, respectively. In test C the subjects performed two exercise bouts each lasting 4.5 min, with work loads of 4.0 W X kg-1. All the exercise bouts were separated by 1-min periods of rest. Exercise B of constant low intensity resulted only in a small increase in plasma noradrenaline concentration. Exercise A of graded intensity caused an increase in both catecholamine levels, whereas, during the most intensive exercise C, significant elevations in plasma noradrenaline, adrenaline and testosterone concentrations occurred. A significant positive correlation was obtained between the mean value of plasma testosterone and that of adrenaline as well as noradrenaline during exercise. It is concluded that both plasma testosterone and catecholamine responses to physical effort depend more on work intensity than on work duration or total work output.

Endocrine response to physical efforts with equivalent total work loads but different intensities in man

The purpose of this study was to determine relationships between some exercise-induced neurohormonal changes and either exercise intensity, or its duration, or the total work output. Plasma catecholamine, cortisol, growth hormone and insulin concentrations were measured in healthy male subjects having performed three bicycle-ergometer exercise tests of the same total work output (2160 J kg-1) but differing in intensity and duration. The results showed that during the relatively short exercise plasma noradrenaline, adrenaline and cortisol responses depend more on work intensity than on the total work output. No relationship was demonstrated between the exercise-induced increases in plasma growth hormone concentration and work intensity or its duration, while the plasma insulin concentration was more decreased during the effort of lower intensity, but longer duration than during a short exercise of high intensity.

Mechanism of sympathetic activation during prolonged physical exercise in dogs. The role of hepatic glucoreceptors

It seems likely that depletion of body carbohydrates may account for the rise in the sympathetic activity during prolonged exercise, since glucose given during or before exercise reduces the increase in plasma catecholamines. The aim of the present study was to find out whether the increase in plasma noradrenaline (NA) in response to exercise can be reduced by 1. increasing of the amount of carbohydrate available for metabolism without producing hyperinsulinemia and 2. by inhibition of afferent activity from hepatic glucoreceptors. The study was performed on dogs which exercised whilst receiving either the intravenous fructose infusion (2.2 mmol/min) or a slow glucose infusion (0.25 mmol/min) which was given either via the portal or a peripheral vein. Fructose infusion reduced the muscle glycogen depletion during exercise and reduced the increase in plasma NA and glycerol concentrations without altering the blood glucose or insulin levels. The exercise-induced increases in plasma NA and glycerol concentrations were significantly smaller with intraportal than with peripheral glucose infusion but there were no differences between these two cases in the concentration of glucose in the systemic circulation. These findings indicate that the reduction of the plasma NA response to physical effort under conditions of increased carbohydrate availability cannot be attributed to the inhibitory effect of insulin on sympathetic activity and provide evidence for the participation of hepatic glucoreceptors in the control of the sympathetic activity during exercise.

Sequence dependence of hydrogen exchange kinetics in DNA duplexes at the individual base pair level in solution

The kinetics for hydrogen exchange at individual base pairs in self-complementary deoxydodecanucleotide duplexes have been estimated from NMR saturation recovery measurements on the resolved imino protons as a function of temperature. The imino protons of dA . dT base pairs in the center of the fully alternating d(C-G-C-G-T-A-T-A-C-G-C-G) duplex exchange a factor of 2- to 3-fold faster than the corresponding protons at the same positions in the partially alternating d(C-G-C-G-A-A-T-T-C-G-C-G) duplex. These exchange parameters are a direct measure of the rate constants for transient opening of individual dA . dT base pairs in the dodecanucleotide duplexes and demonstrate faster opening kinetics for the "TATA" box region compared to the related "AATT" segment.

Reduction in peak oxygen uptake after prolonged bed rest

The purpose was to test the hypothesis that the magnitude of the reduction in peak oxygen uptake (VO2) after bed rest is directly proportional to the level of pre-bed rest peak VO2. Complete pre- and post-bed rest working capacity and body weight data were available from three studies involving 24 men (19-24 yr; peak VO2, 2.39-4.80 l . min-1) and 8 women (23-34 yr; peak VO2 1.47-2.58 l . min-1), who underwent bed rest for 14-20 d with no remedial treatments. Regression analysis of percent change in post-bed rest peak VO2 on pre-bed rest peak VO2 with 32 subjects resulted in correlation coefficients (r) of--0.03 (NS) for data expressed in l . min-1 and -0.17 (NS) for data expressed in ml . min-1 . kg-1. Significant correlations were found that supported the hypothesis only when peak VO2 data were analyzed separately from studies that utilized the cycle ergometer, particularly with subjects in the supine position, as opposed to data obtained from treadmill peak VO2 tests. We conclude that orthostatic factors, associated with the upright body position and relatively high levels of physical fitness from endurance training, appear to increase variability of pre- and particularly post-bed rest peak VO2 data, which would lead to rejection of the hypothesis.

Suppression of thirst in dogs with arteriovenous fistula

The aim of the present study was to investigate the effect of moderate continuous overloading of the heart on 24-h water intake (WI), urine (Vu), sodium (UNaV), potassium (UKV), solute (Cosm) and free water (CH20) excretion. The overloading of heart was produced by construction of the fistula (AVF) between the femoral artery and the vena cava inferior. Twenty four hours WI, Vu, UNaV, UKV, Cosm, CH20, as well as central venous (CVP), arterial (MABP) and interstitial (IP) pressure and volume of the extracellular fluid (ECW) were examined before and 1, 2 or 3 months after production of AVF. Daily water intake, and water/food ratio decreased, whereas CVP, MABP and IP increased significantly after production of the fistula. A significant increase in ECW was found 1 month after production of AVF. It is suggested that a moderate overloading of the heart may cause a prolonged decrease in water intake, possibly due to augmentation of the inhibitory input from the cardiovascular receptors.

Plasma catecholamines during exercise-induced bronchoconstriction in bronchial asthma

Plasma levels of adrenaline and noradrenaline during and after submaximal exercise in patients with bronchial asthma were investigated. Three groups were studied comprising 10 patients with exercise-induced bronchoconstriction (EIB), 10 asthmatic patients without EIB and four normal control subjects. Plasma catecholamines were measured at rest, at the end of exercise, and five and 15 minutes after exercise. Changes in airway resistance were assessed by measuring peak expiratory flow rate. Significant differences in catecholamine levels between reacting and non-reacting patients were found. In 10 patients developing EIB adrenaline and noradrenaline levels had risen significantly by the end of exercise and remained elevated up to the fifth minute of recovery. The rise in catecholamine levels in non-reacting asthmatics was insignificant. In control subjects noradrenaline had increased significantly by the end of exercise.

Hyperglycaemic effect of glucagon after prolonged exhausting exercise in dogs

The purpose of this work was to compare the hyperglycaemic effect of glucagon at rest and after prolonged exhausting exercise in dogs. The following doses of glucagon were administered in 10-minute i.v. infusions: 0.1, 0.5, 1.0 micgrogram-kg-1 min-1. Significant differences were demonstrated in the blood glucose level after glucagon administration in doses of 0.1 and 0-5 microgram-kg-1 min-1 at rest as well as after exercise, and glucagon-induced hyperglycaemia was always lower after exercise than at rest. Increasing of glucagon dose from 0.5 to 1.0 microgram-kg-1 min-1 was not followed by a similar increase of the hyperglycaemic response. In additional experiments glucagon was administered together with adrenaline using two combinations of doses: 0.1 micron g-kg-1min-1 of glucagon and 0.25 microgram-kg-1 min-1 of adrenaline or 1.0 microgram-kg-1 min-1 of glucogen and 1.0 microgram-kg-1 min-1 of adrenaline. The hyperglycaemic effects of glucagon and adrenaline were additive at rest and after exercise when low doses of both hormones were used. After prolonged exercise this additive effect was not found when the "saturating" doses of glucagon and adrenaline were used (1.0 microgram-kg-1 min-1). The results obtained suggest that the hyperglycaemic response to glucagon is decreased in dogs after prolonged excise. It seems that this can be partly explained by the changed reactivity of hepatic tissue to this horme after prolonged exercise.

Thyroid hormone-induced changes in body temperature and metabolism during exercise in dogs

Changes in serum total thyroxine concentration (TT4) and the effects of thyroxine (T4) and 3,5,3'-triiodothyronine (T3) injection on plasma free fatty acid (FFA) level and rectal temperature (Tre) responses were measured in six dogs at rest and during 1 h of submaximal treadmill exercise. At rest there were no increases in FFA level or Tre up to 72 h after thyroid hormone treatment. During exercise, 5 h after a single T4 injection (0.1 mg/kg), there was a) a significant increase in TT4, although the resting level was markedly elevated, and b) a significant increase in FFA concentration and Tre above control values. Seventy-two hours after T4 injection there was a similar increase in TT4 during exercise and both FFA and Tre levels were greater than 5-h values. The elevated Tre was not associated with increased plasma Na+, K+, or osmotic concentrations. Compared with T4 data, T3 injection (0.1 mg/kg) resulted in greater increases in FFA level and Tre during exercise; two animals reached 43.1 degrees C. There were no significant differences in the respiratory exchange ratio (R) or O2 uptake between the control and T3 experiments. It was concluded that thyroid hormones markedly enhance FFA mobilization and elevated Tre during exercise, but not a rest. The hyperthermic response appears to be due to an increase in the level of regulated body temperature rather than to a depression of heat dissipation.