Killing of human cytomegalovirus-infected fibroblasts by antiviral antibody and complement

Complement-dependent cytolytic antibodies (CyAb) to cytomegalovirus (CMV)-infected fibroblasts were detectable in acute- and convalescent-phase sera from renal allograft recipients (n = 44) and nonimmunocompromised patients (n = 14) with symptomatic CMV infection but not in sera from control donors (n = 75; P less than .001 by Wilcoxon rank sum test). Renal allograft recipients with secondary CMV infection had the highest levels of CyAb activity. Activity closely correlated with the serum antibody titer to CMV membrane antigens (r = .9106 by linear regression analysis) and was present in both the IgM and IgG fractions of human sera. IgG F(ab)2 fragments were inactive, thus implicating the classical pathway of complement activation. Maximal CMV-specific lysis was obtained with target cells expressing CMV late membrane antigens (greater than or equal to 72 hr after inoculation) irrespective of the CMV strain used. Adsorption and cold target inhibition studies indicated that the target antigens for the CyAb response are specific for the plasma membrane of CMV-infected cells and may only partly be shared by the virion envelope.

Cytomegalovirus immunity in allogeneic marrow grafting

IgM and IgG class antibodies to cytomegalovirus (CMV) late antigen were studied in 58 bone marrow transplant (BMT) recipients and their donors using a sensitive enzyme-linked immunosorbent assay (ELISA) and with standard virological and histomorphological techniques. Patients who were CMV-seropositive before BMT had a significantly higher risk for active CMV infection after BMT than seronegative ones (23 of 29 vs. 3 of 26 patients; P less than 1 X 10(-6)). Transplantation of marrow from CMV-seropositive donors was associated with a higher incidence of active CMV infection after BMT than transplantation of marrow from seronegative donors (17 of 28 vs. 9 of 27 patients). Such transplantations also had a significantly higher incidence of grades II-IV acute graft-versus-host disease (23 of 29 vs. 11 of 27 patients; P = 0.007). Following BMT, the evolution of the IgG class CMV antibody response was influenced by the serological status of the marrow donor. First, a fall in IgG class CMV antibody titers during the first month after BMT was seen less often after transplantation of marrow from seropositive donors than after transplantation of marrow from seronegative donors. Second, recipients of marrow from CMV-seropositive donors who developed active CMV infection had an earlier IgG antibody response than those with seronegative marrow donors. These results suggest that the transfer of memory B and T cells occurs with the graft. Failure to mount a sustained IgM or IgG antibody response upon active CMV infection was associated with a fatal outcome.

The effect of cytomegalovirus infection on T lymphocytes after allogeneic bone marrow transplantation

The influence of cytomegalovirus (CMV) infection on peripheral T lymphocyte repopulation was studied in 59 bone marrow transplant (BMT) recipients who received either cyclosporin A (CyA) or methotrexate (MTX) as prophylaxis for acute graft-versus-host disease. We used monoclonal antibodies and single- or double-marker immunofluorescence for the quantitation of T4+, T8+ and HNK1+ T cell subpopulations. CMV infection was serologically diagnosed by an enzyme-linked immunosorbent assay (ELISA), and by viral cultures and histological studies. Among the 52 patients who were evaluable for CMV infection, one had a primary infection and 24 had CMV reactivation/reinfection after BMT. In the latter patients, increases to supranormal levels were observed in T8+ T cells and HNK1+ T cells, both in patients on CyA and in patients on MTX. Double-marker immunofluorescence revealed that the two markers were largely expressed by the same cells, which therefore had the T8+ HNK1+ phenotype. In addition, the very small subset of T4+ HNK+ T cells was slightly, but consistently, increased in the patients with CMV reactivation/reinfection. CMV infection did not influence the numbers of T4+ HNK1- and T8+ HNK1- T cells. The long-lasting presence of large numbers of T8+ HNK1+ T cells in patients who had CMV reactivation/reinfection suggests a continuing interaction between the virus and the immune system of its host.

HLA-DRw6 as a risk factor for active cytomegalovirus but not for herpes simplex virus infection after renal allograft transplantation

To study genetically determined susceptibility to cytomegalovirus and herpes simplex virus infections in patients given renal transplants a prospective study was performed of 68 consecutive patients receiving their first cadaveric kidney allograft. The recipients positive for HLA-DRw6 showed a significantly increased incidence of active cytomegalovirus infection as early as the 10th week after transplantation (p less than 0.05). No relation with other human leucocyte antigens was found, nor did a correlation exist between HLA typing and the incidence of herpes simplex virus infections. Furthermore, recipients positive for HLA-DRw6 with secondary cytomegalovirus infections excreted infectious virus more often (p less than 0.01) and showed more clinical symptoms (p less than 0.01) than a comparable group of recipients negative for HLA-DRw6. These observations may have practical implications for the treatment of patients who have had renal transplant operations.

Recovery of T cell subsets after autologous bone marrow transplantation is mainly due to proliferation of mature T cells in the graft

In 22 patients with malignancies, treated with high-dose chemoradiotherapy and autologous bone marrow transplantation (BMT), peripheral blood T cell subsets and functions were studied. In ten cytomegalovirus (CMV)-negative patients, CD4+ and CD8+ T cells (representing T cells of the helper/inducer phenotype and T cells of the suppressor/cytotoxic phenotype, respectively), recovered slowly and simultaneously. In 12 CMV-positive patients, however, CD8+ T cells recovered more rapidly than CD4+ T cells and rose to increased counts. No T cells with an immature phenotype (CD1+, OKT6+) were observed. Lymphocyte stimulation by herpes simplex virus infected fibroblasts (and by CMV-infected fibroblasts in CMV-positive patients) in contrast remained high and even increased after BMT in both groups. These data indicate that T cell recovery after autologous BMT is mainly due to proliferation of mature T cells present in the BM graft and not to generation of new T cells from T cell precursors.

Maintenance of cytomegalovirus (CMV) latency and host immune responses of long term renal allograft survivors. II. Secondary CMV infections associated with impaired in vitro proliferative responses to mitogens, allogeneic lymphocytes and CMV infected cells

The relationship between secondary cytomegalovirus (CMV) infections and host general cellular immunocompetence was investigated in 16 renal allograft recipients with minimal immunosuppressive treatment and excellent renal function. Results were compared with 19 CMV seropositive healthy controls. Significantly impaired immune responses were detected in the subgroup of nine recipients who experience at least 2 years before a secondary CMV infection. Their in vitro lymphocyte reactivity (LR) tests to phytohaemagglutinin (PHA, P = 0.01), pokeweed mitogen (PWM, P less than 0.05), microbial antigens (P less than 0.001) and to pooled allogeneic stimulator lymphocytes in the MLC test (P = 0.02) were lower than the controls. The MLC responses, however, increased with graft survival time (r = 0.8810, P = 0.01). This was positively correlated with the virus specific cellular immunity measurable by the LR responses to CMV infected target cells (r = 0.8333, P = 0.02). In contrast, long term renal allograft survivors who maintained their CMV infection in latency after transplantation (n = 7) showed normal responses to PWM, pooled lymphocytes and CMV infected target cells, whereas the responses to PHA and to bacterial antigens were less severely impaired (P less than 0.05 and P less than 0.001, respectively). This study of long term renal allograft survivors shows that a secondary CMV infection has a long lasting negative effect on immunity especially against alloantigens and CMV infected targets. However, in the data presented here it would be as acceptable to suggest that the patients are consistently relapsing with CMV because they initially had poor immune response and not vice versa.

Maintenance of cytomegalovirus (CMV) latency and host immune responses of long term renal allograft survivors. I. Prolonged suppression of in vitro lymphocyte responses against CMV infected fibroblasts related to previous secondary CMV infection

Cytomegalovirus (CMV) specific humoral and cellular immunity was investigated in 16 renal allograft recipients with long term graft survival (26-122 months) who were shown to be CMV seropositive before transplantation. Results were compared with healthy individuals with latent CMV infections. Recipients (n = 9) who experienced a symptomatic secondary CMV infection shortly after transplantation (less than 6 months), showed a prolonged but finally temporary suppression of their in vitro lymphocyte memory responses against CMV infected fibroblasts (CMV-FF; median SI: 1.9), a persistence of high antibody titres against intracellular CMV antigens and most of them also had antibodies against CMV membrane antigens (CMV MA). In contrast the recipients (n = 7) who could maintain their CMV in latency after transplantation, had lower antibody titres and their in vitro memory lymphocyte responses against CMV-FF (median SI: 9.3) were comparable to those of the healthy controls (median SI: 11.6). The memory lymphocyte responses against purified CMV virions were depressed in both recipient groups. These results suggest that cellular immunity against CMV infected target cells constitute an important mechanism in maintaining CMV in latency after allografting.

Detection of immunoglobulin M and G antibodies against cytomegalovirus early and late antigens by enzyme-linked immunosorbent assay

A sensitive and reproducible enzyme-linked immunosorbent assay (ELISA) is described for the detection of immunoglobulin M and antibodies with specifity for human cytomegalovirus (CMV) early (CMV-EA) and late (CMV-LA) antigens. The emphasis is on the production of high-quality CMV antigens, CMV-EA and CMV-LA separately, and conditions for their application in the ELISA. The induction of CMV-EA and -LA in infected cell extracts was studied in detail by using human sera with defined antibody specificity for CMV-EA and CMV-LA. This resulted in the development of a simple whole cell extraction procedure that provided a high yield of CMV antigens with reproducible antigen quality. The antigens were specific for the detection of anti-CMV antibodies. The influence of autoantibodies on the determination of CMV-specific antibodies was investigated. Parallel analysis of 322 human sera by indirect immunofluorescence and ELISA showed a high correlation between both assays (r = 0.9674 for CMV-EA and 0.9362 for CMV-LA). Antibody titers determined by ELISA were equal to (for CMV-EA) or slightly higher (for CMV-LA) that those determined by immunofluorescence but significantly higher (20- to 5,120-fold) than those determined by complement fixation. From 191 sera positive by ELISA (titer greater than or equal to 40) 4 (2.1%) were negative by immunofluorescence (titer less than 40), and from 61 ELISA-positive sera 12 (19.6%) were negative (titer less than 8) when tested by complement fixation. Consequently, ELISA for CMV may prove to be more reliable for the selection of CMV-seronegative blood donors than these other methods. The use of high-quality antigens allows more economic handling of large-scale serum determinations. Possibilities for further automation are discussed.

An in vitro system to study interactions between bacteria and epithelial cells at the molecular level

This paper describes an experimental system to study interactions between porcine enterotoxigenic Escherichia coli (ETEC) and porcine intestinal epithelial cells in vitro at the molecular level. Radiolabelled bacteria or bacterial membrane fractions were incubated with brush borders prepared from purified epithelial cells, which were then washed repeatedly. The bacterial components removed by washing or retained by the brush borders were analysed to determine their composition and source. For this it was necessary to develop a minimal medium in which attachment factors of porcine ETEC could be radiolabelled. Furthermore, an improved method for the isolation of porcine intestinal epithelial cells was developed, since other procedures did not yield sufficiently pure preparations. The resulting method was rapid and yielded large quantities of viable epithelial cells, free from crypt cells and contaminating intestinal contents. Finally, we adapted existing procedures to isolate brush borders from these epithelial cells with special emphasis on the removal of nuclear and cytosolic material and on the isolation of morphologically intact brush borders. Using this system, mixtures of bacterial cytoplasmic and outer membranes were incubated with brush borders. Cytoplasmic membranes were easily removed by washing, while the outer membranes were not.

A stimulatory role for cytomegalovirus (CMV) antibodies in CMV-specific lymphocyte proliferation in vitro

Cytomegalovirus(CMV)-specific lymphocyte proliferation in vitro was tested in the presence or absence of CMV-specific antibodies. CMV antibodies clearly enhanced CMV-specific lymphocyte proliferation but not lymphocyte proliferation induced by other antigens. Enhancement was most consistently found with cell-bound CMV antigens and often with cell-free CMV as stimulating antigen. CMV antibodies only stimulated when they were added at an early stage of the lymphocyte culture, and the stimulating effect was most pronounced at optimal and suboptimal antigen concentrations. Our data suggest that CMV antibodies stimulate CMV-specific lymphocyte proliferation at the level of antigen presentation.

K88-mediated binding of Escherichia coli outer membrane fragments to porcine intestinal epithelial cell brush borders

We have examined the interactions between various radiolabeled membrane fractions obtained from an enterotoxigenic Escherichia coli strain and brush borders isolated from porcine intestinal epithelial cells. Outer membrane fragments containing the K88 attachment factor bound tightly to brush borders, whereas cytoplasmic membrane vesicles did not. Three different types of outer membrane preparations were tested: (i) cellular outer membranes isolated from lysozyme spheroplasts, (ii) medium vesicles or outer membrane fragments released into the medium during growth, and (iii) periplasmic vesicles, or outer membrane fragments which were released from the cells during spheroplast formation and were therefore isolated in the periplasmic fraction. Of these fractions, which were heterogeneous, it was always the outer membrane subfraction which bound tightly to brush borders. This binding, which was K88 dependent, may have some physiological significance in view of the association between outer membrane fragments and enterotoxin. Thus, released outer membrane fragments equipped with attachment factors may function as enterotoxin carriers which increase the efficiency with which enterotoxin can be delivered to intestinal epithelial cells.