Biological significance of the antibody response to HIV antigens expressed on the cell surface

Mind the Gap: How Interspecies Variability in IgG and Its Receptors May Complicate Comparisons of Human and Non-human Primate Effector Function

The field of HIV research relies heavily on non-human primates, particularly the members of the macaque genus, as models for the evaluation of candidate vaccines and monoclonal antibodies. A growing body of research suggests that successful protection of humans will not solely rely on the neutralization activity of an antibody's antigen binding fragment. Rather, immunological effector functions prompted by the interaction of the immunoglobulin G constant region and its cognate Fc receptors help contribute to favorable outcomes. Inherent differences in the sequences, expression, and activities of human and non-human primate antibody receptors and immunoglobulins have the potential to produce disparate results in the observations made in studies conducted in differing species. Having a more complete understanding of these differences, however, should permit the more fluent translation of observations between model organisms and the clinic. Here we present a guide to such translations that encompasses not only what is presently known regarding the affinity of the receptor-ligand interactions but also the influence of expression patterns and allelic variation, with a focus on insights gained from use of this model in HIV vaccines and passive antibody therapy and treatment.

Conformational Masking and Receptor-Dependent Unmasking of Highly Conserved Env Epitopes Recognized by Non-Neutralizing Antibodies That Mediate Potent ADCC against HIV-1

The mechanism of antibody-mediated protection is a major focus of HIV-1 vaccine development and a significant issue in the control of viremia. Virus neutralization, Fc-mediated effector function, or both, are major mechanisms of antibody-mediated protection against HIV-1, although other mechanisms, such as virus aggregation, are known. The interplay between virus neutralization and Fc-mediated effector function in protection against HIV-1 is complex and only partially understood. Passive immunization studies using potent broadly neutralizing antibodies (bnAbs) show that both neutralization and Fc-mediated effector function provides the widest dynamic range of protection; however, a vaccine to elicit these responses remains elusive. By contrast, active immunization studies in both humans and non-human primates using HIV-1 vaccine candidates suggest that weakly neutralizing or non-neutralizing antibodies can protect by Fc-mediated effector function, albeit with a much lower dynamic range seen for passive immunization with bnAbs. HIV-1 has evolved mechanisms to evade each type of antibody-mediated protection that must be countered by a successful AIDS vaccine. Overcoming the hurdles required to elicit bnAbs has become a major focus of HIV-1 vaccine development. Here, we discuss a less studied problem, the structural basis of protection (and its evasion) by antibodies that protect only by potent Fc-mediated effector function.

Role of Fc-mediated antibody function in protective immunity against HIV-1

The importance of Fc-mediated effector function in protective immunity to HIV-1 (hereafter referred to simply as HIV) is becoming increasingly apparent. A large of number of studies in natural infection cohorts, spanning the last 26 years, have associated Fc-mediated effector function, particularly antibody-dependent cellular cytotoxicity, with a favourable clinical course. These studies strongly suggest a role for Fc-mediated effector function in the post-infection control of viraemia. More recently, studies in both humans and non-human primates (NHPs) also implicate Fc-mediated effector function in blocking HIV acquisition. Accordingly, this review will discuss the results supporting a role of Fc-mediated effector function in both blocking acquisition and post-infection control of viraemia. Parallel studies in NHPs and humans will be compared for common themes. Context for this discussion will be provided by summarizing the temporal emergence of key host and virological events over the course of an untreated HIV infection framing where, when and how Fc-mediated effector function might be protective. A hypothesis that Fc-mediated effector function protects primarily in the early stages of both acquisition and post-infection control of viraemia will be developed.

Development of the antibody response in acute HIV-1 infection

BACKGROUND

Cytotoxic T lymphocytes have been shown to reduce viraemia during acute HIV-1 infection; however the role of neutralizing antibodies in this process is unclear. One confounding factor may be artefacts introduced by viral culture.

OBJECTIVE

To assess the development of autologous neutralizing and non-neutralizing antibodies following acute HIV-1 infection using recombinant viruses with envelopes amplified directly from patient peripheral blood mononuclear cells, thereby avoiding in vitro selection.

METHODS

Disease progression in four homosexual men was monitored from acute infection for up to 2.5 years, in the absence of antiretroviral therapy. Antibodies to viral envelope protein were quantified by enzyme-linked immunosorbent assay. Development of neutralizing antibodies was monitored using a quantitative infectivity reduction assay, sequential serum, recombinant viruses and target cells with defined receptor expression.

RESULTS

The time to development of neutralizing antibodies after onset of symptoms was 3, 5, 7 and 16 months in the four patients. There was no correlation between development of neutralizing antibodies and the resolution of viraemia in any of the patients. However, antibodies to the envelope were detectable as early as 2 weeks after onset of symptoms.

CONCLUSIONS

Neutralizing antibodies do not contribute to the control of viraemia in acute HIV-1 infection. However, antibodies to the envelope could be detected at the time of reduction in plasma viraemia and so other effector functions of antibodies may play a role in viral clearance.

Study of the dynamics of neutralization escape mutants in a chimpanzee naturally infected with the simian immunodeficiency virus SIVcpz-ant

Here we report on the use of spectral map analysis of time-paired sequential neutralization data of 11 serum samples of a chimpanzee naturally infected with a simian immunodeficiency virus (SIVcpz-ant) and 8 primary consecutive SIVcpz-ant isolates, taken at about 4-month intervals. The analysis reveals the existence of three SIVcpz-ant isolate and serum neutralization clusters. Each cluster groups virus isolates and/or sera based on similarities of their neutralization spectra. On average, neutralization escape mutants emerged after 15 months and mounted a neutralization response approximately 8 months later. The entire gp160 regions of eight consecutive isolates were sequenced and analyzed by a new statistical method called polygram, which allowed the deduction of amino acid sequence motifs of gp160 which were specific for SIVcpz-ant isolates belonging to the same isolate neutralization clusters. Changes in specific amino acid quadruplets in V1, V2, C3, V4, V5, and CD4 domains of gp120 and gp40 were seen to correlate with the neutralization clusters with most of the specific changes occurring in the V4 region. This method of analysis may facilitate an understanding of the study of the dynamic interplay between human immunodeficiency virus (HIV) and host neutralization responses as well as providing possible insights into mechanisms of persistence of HIV-1-related lentiviruses in their natural hosts.

Analysis of envelope glycoprotein-specific antibodies from SIV-infected and gp110-immunized monkeys in ACC and ADCC assays

Sera collected from SIV-infected or recombinant glycoprotein-immunized monkeys were characterized for antibodies participating in antibody-complement-mediated cytolysis (ACC) and antibody-dependent cellular cytolysis (ADCC) in terms of their IgG subclass and epitope specificity. In a competitive inhibition ELISA, gp110-specific antibody reactivity with nondenatured rgp110 was blocked completely by soluble homologous rgp110 and partially inhibited by heterologous rgp110, suggesting cross-reactivity between viral strains. However, only partial inhibition was observed with denatured recombinant gp140 (rgp140) in selected monkeys, indicating that the majority of gp110-specific antibodies recognized conformational epitopes. ACC activity against recombinant vaccinia-infected, envelope-expressing targets was found in sera from both infected and immunized monkeys, whereas ADCC activity was observed only in sera from infected monkeys. ACC was blocked with denatured rgp140 as well as nondenatured rgp110, indicating that ACC-mediating antibodies recognized mainly linear epitopes. In contrast, rgp140 did not compete as effectively as rgp110 in the ADCC assay, indicating that the majority of ADCC antibodies recognized conformational epitopes. Competitive inhibition using three peptide fragments of gp110 indicated that epitopes recognized by ACC antibodies lie within amino acid residues 214-471, a region that spans V3, whereas ADCC-reactive epitopes lie between amino acid residues 52 and 214 at the N-terminal end of gp110. Column chromatography of rhesus IgG resulted in three subclass-enriched fractions, designated IgG-I, IgG-II, and IgG-III. IgG-I, but not IgG-II or IgG-III, from both infected and immunized monkeys mediated ACC, whereas IgG-I and IgG-II from infected monkeys mediated ADCC.(ABSTRACT TRUNCATED AT 250 WORDS)

CD3+, CD56+ non-MHC restricted cytotoxic T lymphocytes in two fraternal AIDS patients: a case report

We describe two brothers with hemophilia and AIDS, with an unusually large percentage of CD3+, CD56+ lymphocytes. They experienced no major complications with opportunistic infections (OI) and infrequent secondary infections, even though they had nearly 0% CD4 lymphocytes for 3 years. Both patients died in 1991 of progressive cardiomyopathy. The patients' lymphocytes were immunophenotyped by flow cytometry and analyzed for functional cytolytic activity against K562 and HIV infected HUT 78 cell lines. Single color CD4 counts were 2-9% for 4 years. Dual color CD4 counts at our laboratory demonstrated 0-1% CD4 for the last 6 months. When CD3+ lymphocytes were examined, both patient 1 and patient 2 demonstrated a significantly higher proportion and absolute number of CD3"bright"+, CD56+ double-positive cells, 47% and 22%, respectively, compared to other HIV-positive children with hemophilia (< or = 2%). Functional studies with the K562 target cell line demonstrated the highest natural killer (NK) lymphocyte activity in patient 1 that could not be augmented by in vitro addition of IL-2, whereas patient 2 had no NK activity unless IL-2 was added. Functional studies with HIV-infected HUT-78 cells demonstrated patient 2 had cytolytic activity against HIV-infected cells and patient 1 had high nonspecific cytolytic activity even against uninfected HUT-78 cells, whereas controls had minimal activity to HUT-78 cells or HIV-infected HUT-78 cells. The case report raises a speculative question requiring a larger database, whether the anti-HIV activity and/or unusual clinical course without typical O.I. of some AIDS patients may be related to the presence of CD3"bright"+, CD56+ lymphocytes of their immune system.

Cytotoxic activity against maedi-visna virus-infected macrophages

The cell type predominantly infected by maedi-visna virus (MVV) is the macrophage, and we have looked at the ability of MVV-infected macrophages to interact with cytotoxic T lymphocytes (CTL), important effector cells against virus infections. MVV-specific CTL precursors were detected, after in vitro culture with MVV antigen and recombinant human interleukin-2, in peripheral blood lymphocytes of all MVV-infected sheep. MVV-infected monocyte-derived macrophages and alveolar macrophages were able to stimulate CTL activity in vitro and were targets for these activated CTL. The major effector cell population using MVV-infected macrophage targets was CD8+ lymphocytes, although another population, lymphokine-activated killer cells, may also have been involved. There was no direct cytotoxic activity found in alveolar lymphocytes from MVV-infected sheep without lung lesions.

Anti-lymphocyte antibodies in plasma of HIV-1-infected patients preferentially react with MHC class II-negative T cells and are linked to antibodies against gp41

It has previously been shown that HIV-infected patients develop anti-lymphocyte antibodies. The relationship between anti-lymphocyte antibodies and antibodies against different viral antigens is unknown, and it remains controversial whether some lymphocyte subpopulations are targeted preferentially. We have set out using three-colour flow cytometry to measure antibodies against different lymphocyte subsets. Staining with anti-human immunoglobulin and two MoAbs was performed to characterize the immunoglobulin load of different lymphocyte subsets. Comparison was done between patients' antibody reactivity against HIV-1 antigens and anti-lymphocyte antibodies. We were able to demonstrate the presence of anti-lymphocyte antibodies in approximately 75% of the HIV-infected patients (n = 78) (healthy controls were all negative). MHC class II-negative T cells showed a stronger reaction with anti-lymphocyte antibodies than B cells or MHC class II-positive T cells. Patients with antibodies against CD4 lymphocytes showed a significantly higher antibody reaction with the retroviral antigen gp41 than patients without these antibodies. An association between anti-lymphocyte antibodies and antibody reactivity against other HIV-1 antigens was not noticed. In conclusion, anti-lymphocyte antibodies in HIV-1-infected patients show a preferential reactivity with T cells which lack expression of MHC class II molecules. There is an increased antibody reactivity against gp41 in patients with anti-CD4+ T cell antibodies. The association hints at a specific origin of anti-lymphocyte antibodies in HIV-1-infected patients due to cross-reactivity with viral epitopes or network phenomena. These anti-CD4 cell antibodies could be of interest in the clinical course of HIV infection.

Immune responses induced by prototype vaccines for AIDS in rhesus monkeys

A battery of assay systems was used to profile both humoral and cell-mediated immune responses induced by immunization with candidate vaccines consisting of recombinant simian immunodeficiency virus (SIV) glycoproteins rgp110 (nondenatured) with SAF-M adjuvant (gp110 + SAF-M) or rgp140 (denatured) with Freund's adjuvant (gp140 + FA). All of the monkeys became infected after intravenous challenge. However, 16 days following infection, viral antigenemia was reduced in both groups of vaccinates compared to controls. After 23 days antigenemia in the gp110 + SAF-M group remained at the same level as on day 16, whereas antigenemia in the gp140 + FA group was significantly reduced further than the level observed on day 16. Both vaccines induced blastogenic responses in PBMC cultures stimulated with rgp140, which decreased after repeated immunizations. Both vaccines induced high ELISA titers of IgG antibody against rgp140 that were equivalent to the titers in asymptomatic long-term survivors (LTSs). gp110 +/- SAF-M induced high titers of neutralizing antibody. In contrast, gp140 + FA failed to induce neutralizing antibody, suggesting that the natural conformation of the antigen may be essential for the induction of neutralizing antibody. High titers of antibodies capable of complement-mediated cytolysis (ACC) were induced by gp110 + SAF-M, whereas minimal ACC antibodies were induced by gp140 + FA. In spite of high titers of antibodies by ELISA, neither gp110 + SAF-M nor gp140 + FA vaccines induced detectable levels of antibody capable of antibody dependent cell-mediated cytolysis (ADCC). Detectable amounts of MHC class I-restricted, CD8+ cytotoxic T lymphocytes (CTLs) were not induced in immunized monkeys before challenge. After challenge and infection, antibody responses to glycoprotein (detected by ELISA and ACC) as well as glycoprotein-specific CTLs were induced in gp140 + FA vaccinates at levels higher than in nonimmunized control animals, indicating a priming effect by gp140 + FA immunization. No priming effect for ADCC antibody induction was observed in monkeys vaccinated with either gp110 + SAF-M or gp140 + FA. Rhesus monkey groups immunized with two different SIV envelope vaccines differed regarding potentially protective humoral and cell-mediated immune responses. The physical state of the immunogens, the type of adjuvant used, and/or the immunization protocol apparently affected these responses in both a qualitative and quantitative manner.

Flow cytometric analysis of African swine fever virus-induced plasma membrane proteins and their humoral immune response in infected pigs

African swine fever (ASF) virus-induced plasma membrane proteins may contribute to the protective immune response against the disease since they can be involved in the antibody-mediated lysis of infected cells. In this study we describe the regulation of ASF virus-induced plasma membrane protein expression and its antibody induction in pigs after viral infection by flow cytometric analysis. More than 80% of infected cells contained viral antigens on the surface membranes at 6 hr postinfection (hpi), and the relative amount of viral antigen expression was increased at 12 and 20 hpi. The kinetics of individual viral protein expression on cell surfaces was studied by a collection of monospecific antibodies directed against the six viral plasma membrane proteins p12, p15, p16, p23.5, p30, and p35. Most of these proteins were expressed at 6 hpi, with the exception of p35, which was first detected at 12 hpi. The percentage of cells expressing each antigen at different hpi was also determined. The immune response against virus-induced plasma membrane proteins in pigs infected with an attenuated ASF virus strain was studied. Antibodies against viral epitopes exposed on plasma membranes reached a plateau at 20 days postinfection (dpi). The relative amount of antibodies induced during infection with these specificities was not directly related to the antibody titer of the sera. Sera obtained at 20 and 40 dpi contained antibodies against most of the viral plasma membrane proteins and were most efficient in recognition of viral antigens exposed on the surface of infected cells at early times.

Lack of autologous neutralizing antibodies in the cerebrospinal fluid of HIV-1 infected individuals

The cerebrospinal fluids (CSF) and sera from HIV-1-infected individuals at different clinical stages were monitored for neutralizing activity against CSF-derived HIV-1 isolates. None of the CSF samples and only one of seven serum samples could neutralize the autologous CSF isolate. CSF samples collected one to two years later from the same patients also lacked autologous neutralizing antibodies against these isolates. However, some CSF samples were able to neutralize heterologous CSF isolates albeit in low titers. HIV antibody positive control sera could readily neutralize all of the CSF isolates demonstrating that these isolates were not resistant to neutralization per se. IgG antibodies against the HIV-1 envelope protein and, specifically, against the V3 loop of HIV-1 gp120 (MN) were present in some CSF samples, although the samples lacked neutralizing activity. In summary, this study demonstrates a lack of autologous neutralizing antibodies in CSF samples when assayed against CSF-derived HIV-1 isolates.

Inhibition of HIV-1 infection in vitro by murine monoclonal anti-p24 antibodies

Murine monoclonal antibodies (Mabs) to the major core protein p24 of the human immunodeficiency virus type 1 (HIV-1) were tested for their ability to inhibit the replication and spread of the virus in permanent cell cultures (Molt4/8, K37, H9) and in the culture of II-2 stimulated T cells of healthy donors. After addition of ascitic fluid containing monoclonal anti-p24 antibodies or purified anti-p24 antibodies or the respective control to co-cultures of infected and non-infected cells, HIV-1 replication was evaluated by determining the percentage of infected cells and the activity of reverse transcriptase (RT) in cell-free supernatant. In addition, the supernatant's infectivity was determined. FACS analysis demonstrated p24 antigen in about 40% of unfixed HIV-1 infected cells at the cell membrane. Monoclonal anti-p24 antibodies of different epitope specificity added to the cells but not to the virus delayed the spread of HIV-1 infection in permanent cell culture. Furthermore, anti-p24 Mabs inhibited the release of RT-active virus particles by HIV-1 infected cell lines or II-2 stimulated T-lymphocytes, respectively, up to 60%. The mode of action of anti-p24 antibodies after HIV-1 infection is discussed on the basis of the data obtained.

Humoral immune responses in human HIV-1 infection clearance of initial burst of virus replication and protection against disease progression

An attempt is made to summarize the evidence that humoral immune responses in natural HIV-1 infection play a role in clearance of the initial burst of replication as well as in protection against rapid disease progression. Therefore, the so-called "asymptomatic carrier state" was defined on the basis of immunological characteristics, such as CD4+ cell number, CD45RA-CD29+ cell number, CD4+ proliferative responses to anti-CD3 mAbs and soluble activation markers, as well as virological characteristics such as the state of the viral genome in the cell, levels of genomic RNA production, antigenemia, viremia and virus phenotype. During natural infection two major classes HIV-1 neutralizing and cell-fusion inhibiting antibodies are elicited. One population directed against mostly continuous epitopes localized in the third variable domain (V3) of the envelope and one against discontinuous epitopes of the envelope. The last population blocks gp120-CD4 attachment, the first does not. The role of each of these populations of functional antibodies, in the clearance of viremia and the maintenance of the asymptomatic carrier state is discussed.

Isolate-specific neutralizing antibodies in patients with progressive HIV-1-related disease

Four individuals with increasing severity of HIV-1 infection were studied for serum neutralizing activity against their own virus isolates collected during 1-3 years. Sequential serum samples and HIV-1 isolates were available from these patients from the stage of lymphadenopathy to severe immunodeficiency. The replicative capacity of isolates changed from slow/low to rapid/high in each patient during the study period. Sequential virus isolates showed differences in sensitivity to neutralization by autologous as well heterologous area. Taken together with our previous results demonstrating that variant viruses resistant to neutralization by autologous sera emerge during the year following primary infection, neutralization-resistant variants seem to emerge during the entire course of HIV-1 infection. The ability to produce neutralizing antibodies to autologous virus appears to correlate with replicative capacity of the virus and the degree of immunodeficiency in the patient.

Melatonin-induced enhancement of antibody-dependent cellular cytotoxicity

Antibody-dependent cellular cytotoxicity (ADCC) is a lytic mechanism in which a specific antibody acts cooperatively with leukocytic effector cells to induce target cell lysis. In this paper, the effect of exogenous melatonin on ADCC was examined. It was found that two evening intravenous injections of melatonin (1 mg/kg b.w.) was sufficient to enhance the capacity of splenocytes to mediate ADCC. This augmented activity returned to normal levels by day 6. Moreover, the opioid antagonist, naloxone, was unable to inhibit the ADCC enhancement, suggesting that melatonin did not operate through a naloxone-sensitive opiatergic mechanism. These results further support the modulatory action of melatonin on immune responses.

Immunological dysregulation of lymph nodes in AIDS patients

Changes in immune competent tissues of the HIV-1-infected person reflect to a certain extent the kind and intensity of immunological dysregulations. The diagnostic approach, however, must include immunophenotyping of cells, immunovirological studies of virus distribution in diseased tissues, and functional tests in addition to classical morphology. The latter technique alone just serves as a crude screening method since structural lesions in lymphoid tissues do not permit discrimination from other HIV-independent immune deficiency and autoimmune disorders. Although the overall appearance of lymph nodes in HIV infection and in chronic autoimmune disorders, such as collagen vascular diseases (e.g., rheumatoid arthritis and systemic lupus erythematosus), is similar, immunophenotyping shows a progressive loss of CD4 cells in HIV infection yet a quantitative increase in this cell population in autoimmune disorders (Krueger 1985a). In addition, there are other persistent active infections by lymphotropic viruses (e.g., EBV or HHV-6) which can cause structural and cellular changes in lymphoid tissues closely resembling HIV-induced lesions (Krueger et al. 1988b; Krueger 1985b). The pathological diagnosis therefore nedds to be supplemented by serological studies and--in selected cases--by in situ hybridization for the demonstration of viral genome. Southern blotting for viral DNA can only detect high numbers of viral genome copies in tissue extracts, not in which cell population the virus resides (e.g., malignant cells vs associated "normal" cells), while the polymerase chain amplification reaction, the most sensitive of all (Buchbinder et al. 1988), cannot yet differentiate between latent and (disease-related) active infection. Taking into consideration the above-described precautions in the evaluation of lymphatic lesions, there are a number of characteristic changes which reflect well the sequelae of HIV infection itself and of the ensuing immune dysregulation. Progressive loss of CD4 cells in the paracortex of lymph nodes and in the peripheral blood leads to inversion of the CD4/CD8 ratio. Loss of demonstrable CD4 cells is probably the consequence not only of cell lysis by HIV-1 infection (note: discrepancy between HIV-1 genome positive cell numbers and depletion of CD4 cells) but also of decreased CD4 marker synthesis in infected cells (Stevenson et al. 1987). In this context it is interesting that Fouchard et al. (1986) were able to show HIV expression in CD8 cells and theorized that these developed from infected CD4 cells which subsequently lost the CD4 epitope and expressed CD8.(ABSTRACT TRUNCATED AT 400 WORDS)

Emergence of viruses resistant to neutralization by V3-specific antibodies in experimental human immunodeficiency virus type 1 IIIB infection of chimpanzees

Emergence in two chimpanzees of human immunodeficiency virus type 1 (HIV-1) IIIB variants resistant to neutralization by the preexisting antibody is described. Viruses isolated from the HIV-1 IIIB gp120-vaccinated and -challenged animal were more resistant to neutralization by the chimpanzee's own serum than viruses isolated from the naive infected animal, indicating immune pressure as the selective mechanism. However, all reisolated viruses were 16- to 256-fold more neutralization resistant than the inoculum virus to antibodies binding to the third variable domain (V3) of the HIV-1 external envelope. Early chimpanzee serum samples that neutralized the inoculum strain but not the reisolated viruses were found to bind an HIV-1 IIIB common nonapeptide (IQRGPGRAF) derived from the gp120 isolate-specific V3 domain shown to induce isolate-specific neutralization in other animals. Amplification of the V3 coding sequence by polymerase chain reaction and subsequent sequence analysis of the neutralization-resistant variants obtained from in vivo-infected animals indicated that early resistance to neutralization by an HIV-1 IIIB monoclonal antibody (0.5 beta) was conferred by changes outside the direct binding site for the selective neutralizing antibody. The reisolated neutralization-resistant isolates consisted of the lower-replication-competent virus subpopulations of the HIV-1 IIIB stock, as confirmed by biological and sequence analyses. In vitro passage of the HIV-1 IIIB stock through chimpanzee and human peripheral blood mononuclear cell cultures void of HIV-specific antibody resulted in homogenic amplification of the more-replication-competent subpopulation preexisting in the original viral stock, suggesting a role for the immune system in suppressing the more-replication-competent viruses.

Failure of ADCC to predict HIV-associated disease progression or outcome in a haemophiliac cohort

Antibody-dependent cell-mediated cytotoxicity (ADCC) has been described in a number of virus infections and occurs in HIV infection. In spite of numerous studies on the ability of HIV-positive sera to mediate ADCC, it remains unclear whether ADCC has any functional significance. Here we examine serial serum samples from a cohort of haemophilia patients who became infected from a common source in 1984, and show that there is no significant difference in ADCC values between those who remained asymptomatic and those who progressed to disease. This study does not compare effector cell function and clinical status and does not exclude activity against different target cell lineages in vivo.

HIV-1-specific antibodies in cerebrospinal fluid mediate cellular cytotoxicity and neutralization

Antibodies mediating HIV-1-specific cellular cytotoxicity (ADCC) and virus neutralizing activity were detected in the cerebrospinal fluid (CSF) and, as previously reported, in sera of subjects with varying severity of HIV-1 infection, including patients with or without neurologic or psychiatric symptoms. ADCC-mediating antibodies against target cells infected with the HTLV-IIIB strain of HIV-1 were less frequently present in CSF than in sera, 32 and 60%, respectively. The frequency of ADCC-positive CSF was comparable for the different clinical stages of the disease and was apparently not influenced by the presence or absence of neurologic/psychiatric symptoms. Virus-neutralizing activity was tested against HTLV-IIIB and one CSF-derived viral isolate. Serum antibodies neutralized HTLV-IIIB more frequently than the CSF isolate, 53 and 35%, respectively. In contrast, only three (7%) of the CSF specimens contained neutralizing activity to the CSF-derived isolate and none to HTLV-IIIB. Despite an intact blood-brain barrier in many subjects, the serum/CSF ratios of ADCC or neutralizing antibodies were lower than normally expected. This indicates that both ADCC-mediating and virus neutralizing antibodies may be intrathecally synthesized. Whether these antibodies are protective against or contribute to the histopathologic changes in the brain is not known at present.