The role of oxidative imbalance in progression to AIDS: effect of the thiol supplier N-acetylcysteine

In this study we investigate the redox profile of HIV+ patients at different stages of disease with regard to immunological parameters, i.e., the number of circulating CD4+ and CD8+ lymphocytes. For this purpose, peripheral blood mononuclear cells (PBMCs) obtained from healthy donors, HIV+ patients in the asymptomatic phase, long-term nonProgressors (LTNPs), and AIDS patients have been considered. Cells have been exposed in vitro to the prooxidizing agent menadione, which is able to induce superoxide anion formation, and the susceptibility of the cells to the induced oxidative stress was estimated. Moreover, the possibility that the susceptibility of the cells to oxidative stress might be reduced by preexposing them to the antioxidizing agent N-acetylcysteine (NAC) has also been analyzed. The results obtained can be summarized as follows: (1) treatment with the prooxidant agent is capable of inducing massive morphological alterations in PBMCs. In particular, a significant correlation was found between the decrease in number of CD4+ lymphocytes in patients at different stages of disease and the susceptibility of their PBMCs to oxidative stress; (2) preincubation with NAC was able to preserve partially the ultrastructural characteristics of PBMCs isolated from HIV+ patients. In particular, a direct relationship was found between the efficacy of NAC protection and CD4 counts; (3) evaluation of the plasma index of peroxidation and the number of circulating CD4 lymphocytes indicates the existence of a positive correlation between "systemic" oxidative imbalance and stage of the disease; and (4) cells from LTNPs display either oxidative susceptibility or oxidative markers similar to those of healthy donor cells. Our study suggests that the redox profile of patients may be considered a predictive marker of AIDS progression and that the acute infection and the asymptomatic phase of the disease may represent a useful period in which the combined use of antiretroviral and antioxidant drugs may be beneficial.

Specific IgE antibodies in the diagnosis of atopic disease. Clinical evaluation of a new in vitro test system, UniCAP, in six European allergy clinics

A new immunoassay system utilizing new automatic instrumentation, new software for evaluation of data, and reagents updated for increased speed and accuracy was evaluated. Six clinical studies included 894 consecutive patients. Major symptoms were rhinoconjunctivitis, asthma, atopic dermatitis, and urticaria. The prevalence of inhalant allergy was 54-69%. Phadiatop, detecting atopic sensitization to common inhalant allergens, agreed with clinical diagnosis in 764/836 cases (91.4%). The clinical sensitivity and specificity were 93% and 89%, respectively. The clinical sensitivity and specificity of UniCAP specific IgE derived from 5170 comparisons with clinical diagnosis were 89% and 91%, respectively. Specific IgE measurements in UniCAP and in the Pharmacia CAP System agreed in 266/274 cases (97%). A comparison of the sensitivity and specificity of Pharmacia CAP System RAST in 1987 and with UniCAP specific IgE in 1995 showed equivalent performance without change of efficacy or degradation of IgE antibodies after 8 years. The systems were equivalent also in terms of measured values (r=0.96, slope=1.12), confirming the standardization of allergens and of assay calibration. UniCAP is an efficient laboratory system for routine diagnostic testing of allergy and a valuable tool for basic studies on allergens and antibodies.

Lymphocyte activation gene-3 (LAG-3) expression and IFN-gamma production are variably coregulated in different human T lymphocyte subpopulations

We evaluated the relationship between cytokine profile and the expression of the lymphocyte activation gene-3 (LAG-3) in both T cell clones and polyclonal T cell lines; LAG-3 is a CD4-like protein whose expression is reportedly restricted to Th1/0 cells and dependent upon IFN-gamma. We found that, while LAG-3 was expressed only by CD4+ T cell clones producing IFN-gamma, most CD8+ clones producing IL-4 but not IFN-gamma (i.e., with a T cytotoxic-2-like profile) were LAG-3+. The intensity of LAG-3 expression by CD8+ clones correlated with the amount of released IFN-gamma, suggesting that this cytokine is not required for expression but rather for the up-regulation of LAG-3. Flow cytometric analyses of polyclonal T cell lines confirmed that LAG-3 could be expressed by both CD4+ and CD8+ cells that did not contain cytoplasmic IFN-gamma. In these cell lines, large proportions of CD4+ and CD8+ cells coexpressed LAG-3 and CD30, a putative marker of Th2-like cells. Overall, our data do not support the earlier suggestion that LAG-3 and CD30 are selective markers of T cells with type-1 and type-2 cytokine profiles, respectively.

HIV-1 nef mutations and clinical long-term nonprogression. A molecular epidemiology study

OBJECTIVES

To analyze HIV-1 nef gene mutations in a cohort of Italian and Swedish long-term nonprogressors (LTNP) and to investigate whether particular amino acid substitutions are associated with LTNP.

STUDY DESIGN/METHODS

nef alleles from 21 LTNP and 8 progressor controls were amplified by polymerase chain reaction (PCR) and sequenced. The amino acid sequences were compared with the previously reported sequences of 16 North American LTNP and of 28 patients with progressive infection.

RESULTS

An untruncated intact open reading frame was observed as major sequence in all LTNP and controls. None of the amino acid substitutions in known biologically functional sites was linked to LTNP. A valine/isoleucine at the variable position 11 was associated with both European (P = .0001) and American (P = .001) LTNP. The interpatient nef variation was lower among European LTNP (P = .002) than in European progressor controls.

CONCLUSIONS

Nef amino acid heterogeneity is lower among LTNP, probably reflecting the lower HIV-1 replication rate. Nef gene defects appear uncommon in both Swedish and Italian LTNP, although the presence of a valine/isoleucine at position 11 is statistically associated with a lower probability to progress to disease.

HCV infection in Egyptian patients with acute hepatitis

The diagnostics of community-acquired acute HCV hepatitis in an endemic area was studied in 110 Egyptian patients with acute jaundice. In the first week of the jaundiced period 30 of 110 patients (27.3%) had anti-HCV antibodies. The majority already showed high levels of anti-HCV IgG (25/30), associated with anti-HCV IgM in nine of them. Five patients showed only an HCV IgM reactivity. Seven had also anti-HEV and/or anti-HBV: their jaundice could then be related to an acute infection caused by those viruses. All patients were infected with genotype 4a, in three associated with the 3a. During the follow-up five patients seroconverted for IgG, while their anti-HCV IgM did not show a uniform pattern of reactivity. Patients with positive serology suspected of an acute HCV infection were older than the patients with other acute hepatitis and showed a lower peak of ALT level. Seroconversion during acute hepatitis strongly indicated HCV as the etiologic agent. However, the detection of anti-HCV IgG antibodies in the jaundiced period showed that the majority of patients had already seroconverted to anti-HCV antibodies; in most of them it is possible to hypothesize a reactivation of a chronic HCV infection.

CD28 costimulation and T lymphocyte proliferative responses in HIV-1 infection

To investigate whether defective costimulatory signals could be involved in the loss of T lymphocyte functions during HIV-1 infection, we tested the effect of CD28 costimulation on both T cell receptor/CD3 and HIV-1 antigen-induced proliferative responses. Although CD3-mediated responses significantly decreased with more advanced stages of HIV-1 infection, the ability of potentiating the responses through CD28 costimulation was maintained at all stages and did not differ from that of HIV-1- subjects. When CD28 costimulation was studied in lymphocyte cultures stimulated with HIV-1 gp160 or p24, potentiation was seen only when a significant response was present without additional CD28 triggering, namely in subjects receiving active immunization with recombinant gp160. These results confirm the integrity of the CD28 pathway of costimulation during HIV-1 infection, and suggest that lymphocytes responding to soluble HIV-1 antigen are not deleted in HIV-1-infected patients, but do not receive significant priming during the natural course of the infection.

Eosinophil-derived proteins in postprandial (food-dependent) exercise-induced anaphylaxis

BACKGROUND

Postprandial exercise-induced anaphylaxis (PPEIAn) is a form of EIAn in which the ingestion of food before the exercise is associated with the onset of symptoms. Skin reactivity and the presence of specific serum IgE to several food allergens suggest the occurrence of food-dependent allergic mechanisms.

METHODS

In order to study the involvement of eosinophils in the pathogenesis of PPEIAn we measured the changes in serum eosinophil cationic protein (ECP) and eosinophil protein X/eosinophil-derived neurotoxin (EPX/EDN) levels in 6 patients with PPEIAn, subjected to three separate challenges with either suspected foods only, exercise after a meal without or with suspected food ingestion.

RESULTS

We found serum levels of both eosinophil-derived proteins increased only in challenges including both exercise and suspected food ingestion. Symptoms of anaphylaxis occurred in 3 of these patients.

CONCLUSIONS

The increased release of eosinophil basic proteins in PPEIAn patients, caused by physical exercise following ingestion of suspected foods, is not obligatory for the definition of the syndrome.

IL-10 production and CD40L expression in patients with common variable immunodeficiency

The authors studied CD40 ligant (CD40L) expression and interleukin-10 (IL-10) production in 16 patients with common variable immunodeficiency (CVI). Mean CD40L expression, determined by using cytofluorimetry, and measured as the mean fluorescence intensity following stimulation of peripheral blood mononuclear cells (PBMC) with phorbol myristate acetate (PMA) and calcium ionophore in 12 patients, was comparable to that of controls. However, three CVI patients showed fluorescence intensity in stimulated cells below 2 standard deviations of normal donors' mean and two other patients had only a slight increase of stimulated versus unstimulated cells (< 10 channels). IL-10 production after stimulation of PBMC with both anti-CD3 or anti-CD3 plus PMA gave similar results in CVI patients and normal controls. In vitro stimulation of PBMC with anti-CD40 and various combinations of cytokines (IL-2, IL-4 and IL-10) induced IgG production above 100 ng/ml in one CVI patient out of 13 tested. The data suggest that alterations of IL-10 production are unlikely to play a major role in the pathogenesis of impaired IgG production in most CVI patients. CD40L appears to be normally expressed in two thirds of CVI patients, but it may be functionally defective.

C-C chemokines, IL-16, and soluble antiviral factor activity are increased in cloned T cells from subjects with long-term nonprogressive HIV infection

A combination of three beta, or C-C, chemokines, as well as IL-16, have been shown to inhibit HIV replication in vitro. Cellular antiviral factor is a more potent agent, and acts on all HIV strains. All are mainly, but not exclusively, produced by CD8+ T cells, both in HIV+ and healthy subjects. We studied the production of these HIV-suppressive factors in patients with HIV infection at different stages of disease. No difference in production by PBMC stimulated with PHA has been observed in asymptomatic HIV+, long-term nonprogressors (LTnP), and AIDS patients. When T cell line supernatants from these three groups were studied, no significant difference was found for C-C chemokines or IL-16 production, and viral suppression. However, T cell clones from LTnP secreted higher levels of all three chemokines, IL-16, and exerted a stronger inhibition on HIV replication. CD8+ clones showed a higher production than CD4+ clones. These clones were able to produce all antiviral factors irrespective of the secretion of type 1 or type 2 cytokines. The antiviral activities were not correlated, implying that viral suppression did not depend solely on C-C chemokines or IL-16. We postulate that all factors are needed to prevent HIV disease progression.

C-C chemokines, IL-16, and soluble antiviral factor activity are increased in cloned T cells from subjects with long-term nonprogressive HIV infection

A combination of three beta, or C-C, chemokines, as well as IL-16, have been shown to inhibit HIV replication in vitro. Cellular antiviral factor is a more potent agent, and acts on all HIV strains. All are mainly, but not exclusively, produced by CD8+ T cells, both in HIV+ and healthy subjects. We studied the production of these HIV-suppressive factors in patients with HIV infection at different stages of disease. No difference in production by PBMC stimulated with PHA has been observed in asymptomatic HIV+, long-term nonprogressors (LTnP), and AIDS patients. When T cell line supernatants from these three groups were studied, no significant difference was found for C-C chemokines or IL-16 production, and viral suppression. However, T cell clones from LTnP secreted higher levels of all three chemokines, IL-16, and exerted a stronger inhibition on HIV replication. CD8+ clones showed a higher production than CD4+ clones. These clones were able to produce all antiviral factors irrespective of the secretion of type 1 or type 2 cytokines. The antiviral activities were not correlated, implying that viral suppression did not depend solely on C-C chemokines or IL-16. We postulate that all factors are needed to prevent HIV disease progression.

HCV infection in a patient with hyper IgM syndrome

The association between an acquired form of hyper-IgM syndrome and a chronic hepatitis C virus (HCV) infection in a 71-year-old female patient is described. Both diseases were diagnosed at the age of 58 years. She was started on intramuscular and then intravenous immunoglobulin replacement therapy. HCV RNA was detected in 1992. The patient remained in well-balanced clinical condition until 1994, when total and specific anti-HCV IgM levels increased and the patient developed an IgM kappa monoclonal gammopathy. Adherent cells and B cells were HCV RNA positive, while T cells were HCV RNA negative. Anti-IgM reactivity was specifically directed to the core antigen of the HCV. The patient we describe showed a picture of a late-onset form of hypogammaglobulinemia with a progressive increase in IgM antibodies, possibly due to the concomitant HCV infection. It is possible that the immunodeficiency might also result from the HCV infection, with formation of specific antibodies belonging to the IgM class, and that the worsening of the clinical condition may be directly related to the persistent viral infection.

A shift to Th0 cytokine production by CD4+ cells in human longevity: studies on two healthy centenarians

Centenarians, particularly healthy centenarians, constitute the example of successful aging and the study of their immune status can help to define the endpoint of the changes occurring throughout life. We characterized T cell clones (TCC) of two healthy centenarians, studying their phenotypes and production of representative Th1 and Th2 cytokines (IFN-gamma and IL-4) and compared them with TCC obtained by three young normal subjects; in all 180TCC were analyzed. In young donors, 35TCC were CD4+, 56CD8+ and 2 were alpha beta +CD4-CD8- (double negative). In centenarians, we obtained 46CD4+TCC, 38CD8+, 2CD4+CD8+ (double positive) and 1 gamma delta + double negative. Of the young subjects' TCC, 71% produced IFN-gamma but no IL-4 (Th1 pattern) and this prevalence decreased to 39% in TCC from the centenarians. The number of clones showing the opposite Th2 pattern was similar in young and aged donors (3 out of 93TCC and 2 out of 87TCC, respectively). The intermediate profile of TCC producing both IL-4 and IFN-gamma (Th0) was found in 25.8% of clones from young people, but it almost doubled to 58.6% in centenarians. The analysis shows that the Th profiles of CD8+TCC is nearly superimposable in the two groups, whereas a major shift from a Th1 to a Th0 pattern is presented by CD4+TCC. The balance provided by a majority of CD4+TCC showing a Th0 pattern may ensure both humoral and cell-mediated defences. In CD8+TCC, however, a Th1 pattern still is present, possibly for efficient generation of cytotoxic responses. These findings should be extended by studying other centenarians and elderly subjects.

CD45 isoforms expression on CD4+ and CD8+ T cells throughout life, from newborns to centenarians: implications for T cell memory

CD4+ and CD8+ peripheral blood T lymphocytes show mutually exclusive expression of CD45RA or CD45R0, two isoforms of the common leukocyte antigen that seem to recognize so-called virgin/unprimed and memory/activated T cells. The expression of these isoforms has been studied by three colour cytofluorimetric analysis on CD4+ or CD8+ peripheral blood CD3+ cells from 22 healthy centenarians, analyzed in a context of 202 healthy donors 0-110 years old. An age-related unbalance of virgin and memory cells was found between CD4+ and CD8+ subsets. As expected, at birgh 95-99% of the CD3+ lymphocytes expressed the CD45RA isoform. A rapid increase of CD45R0+ cells was observed in the first 2-3 decades of life, this phenomenon being much more pronounced on CD4+ cells. Subsequently, the increase of the 'memory' compartment was much less rapid, so that in centenarians a consistent reservoire of CD45RA+ among CD4+ cells was still present (about 20%). In these exceptional individuals the percentage of CD45RA+ cells among CD8+ T lymphocytes was even higher (about 50%), and only slightly lower than that of young donors (about 55-60%). Thus, the main changes occurred at a different rate in CD4+ (about 20%). In these exceptional individuals the percentage of CD45RA+ cells among CD8+ T lymphocytes was even higher (about 50%), and only slightly lower than that of young donors (about 55-60%). Thus, the main changes occurred at a different rate in CD4+ and in CD8+ T cells, at an age of between 0 and 30 years, when the thymus is still functionally active. Interestingly, no difference in the usage of CD45 isoforms was observed within T cells bearing four different V beta-T cell receptor (TCR). The significance of this age-related unbalance is unknown. However, the presence of a great number of CD45RA+ T lymphocytes within the CD4+ and the CD8+ T cell subsets even in the peripheral blood of centenarians poses the problem of their origin (thymus? extrathymic sites?), of their functional role and of their lifespan. Moreover, the data on centenarians suggest that they may represent a very selected population where a slowing of immunosenescence occurs.

Hepatitis C virus infection in Italian patients with hypogammaglobulinemia

We investigated the presence of hepatitis C virus (HCV) infection in 58 patients with humoral immunodeficiencies. Forty-three of these patients had common variable immunodeficiency (CVI), 2 had sporadic hyperimmunoglobulin M (HIM) syndrome, 2 had immunoglobulin G subclass deficiency, 4 had ataxia-telangiectasia (AT), and 7 had X-linked agammaglobulinemia (XLA). Patients with late-onset hypogammaglobulinemia (those with CVI, HIM, or immunoglobulin G subclass deficiency) had a 38.2% prevalence of HCV infection. In patients with XLA or AT, HCV infection was not detectable. Most of the HCV-infected patients had persistent viremia, with histologic findings of chronic hepatitis. Although patients positive for HCV ribonucleic acid (RNA) had received several lots of immunoglobulin, we were unable to detect any correlation between the time that alanine aminotransferase levels increased and the time that intravenous immunoglobulin therapy was given, except in one patient with CVI. Moreover, we found no differences in the number of blood transfusions, surgical procedures, or administrations of intravenous or intramuscular immunoglobulin between HCV RNA-positive and HCV RNA-negative groups. We concluded that: (1) the incidence of HCV infection in patients with hypogammaglobulinemia is much higher than that reported in the Italian general population; (2) although patients with hypogammaglobulinemia have persistent viremia, they do not show an aggressive course of HCV disease, nor does hepatocarcinoma develop; and (3) intravenous immunoglobulins are only one of several possible causes of HCV transmission in patients with humoral immunodeficiencies.

Expansion of CD11abright cells in CD8+CD45RA+ from HIV-infected patients: a new early marker for disease progression?

CD8+CD45RA+ T lymphocytes present two distinct subpopulations expressing the CD11a molecule (LFA-1 alpha chain) with different intensity. CD11adim cells represent the unprimed population within the CD8+CD45RA+ subset, whereas CD11abright cells are activated and may be considered as memory lymphocytes. The aim of this study was to analyze the expression of CD11a and CD18 within the CD8+CD45RA+ population in young HIV-infected individuals at different stages of disease as a marker of activation and of disease progression. Blood cells from 82 HIV-infected individuals and 23 age-matched healthy controls were stained with unconjugated CD11a, CD18, PE-goat F(ab')2 anti-mouse, FITC-CD45RA, and TRI-Color CD8. Quantitative analysis for three-color immunofluorescence was carried out by flow cytometry. HIV+ subjects were subdivided into three groups according to their CD4+ cell number (group A, CD4+ cells > 500/microliters [20 subjects], group B, CD4+ cells between 500 and 200/microliters [36 subjects], and group C, CD4+ lymphocytes < 200/microliters [26 subjects]). We found a significant increase of CD11abright in the CD8+CD45RA+ subpopulation throughout the progression of the disease. The CD11abright percentage of positivity (mean) within the CD8+CD45RA+ subpopulation was 31% in healthy donors, 51% in group A, 52% in group B, and 68% in group C. CD11abright expression was closely related to CD18bright (p < 0.001), but not to CD38. The relative increase of CD11a and CD18 expression in CD8+CD45RA+ T lymphocytes parallels the decrease of CD4+ cells and the progression of disease: an inverse correlation between the percentages of CD4+ cells/microliter and CD8+CD45RA+CD11abright cells (p < 0.001) and a direct correlation between the number of CD4+ lymphocytes per microliter and both the number of CD8+CD45RA+CD11adim cells (p < 0.001) and the number of CD8+CD45RA+CD11abright (p = 0.002) was observed. The relative increase of CD8+CD45RA+CD11abright cells may represent an additional marker for monitoring HIV-induced immunodeficiency.

Family and linkage study of selective IgA deficiency and common variable immunodeficiency

Screening of close relatives of Swedish patients with selective immunoglobulin A deficiency (IgAD) and common variable immunodeficiency (CVID) for serum immunoglobulin levels has identified the positive family history of IgAD/CVID as the most significant risk factor for developing the disease. The relative risk for siblings of patients with IgAD was estimated to be approximately 50. In 12 of 34 Swedish multiplex families identified in the study, both IgAD and CVID occurred, usually CVID in the parental generation and IgAD in the subsequent generation. This proportion was much higher than expected by chance and strongly suggests that the two clinically discernible disorders represent an allelic condition, reflecting a variable expressivity of a common defect. In 27 multiplex families the disorders segregated as an autosomal dominant trait, affecting at least two generations. A high relative risk for siblings, permanent phenotype, low number of phenocopies, and common population prevalence, which makes it possible to obtain a sufficient sample size, make these immunoglobin deficiencies amenable to genetic linkage analysis. In a pilot multicenter linkage study involving 16 multiplex families with dominant transmission of IgAD/CVID, we have attempted to confirm previously reported genetic linkage of the disease susceptibility to the major histocompatibility complex (MHC) region. Using both parametric and nonparametric linkage analyses with a set of microsatellite markers at and flanking the MHC region, no evidence for linkage was found. In accordance with these results, no evidence for linkage to the MHC region was obtained by analyzing previously published segregation data at the MHC region in multiplex families with IgAD/CVID in more than one generation.(ABSTRACT TRUNCATED AT 250 WORDS)

HCV infection in patients with primary defects of immunoglobulin production

We tested for infection with hepatitis C virus (HCV) in 58 patients affected by humoral immunodeficiencies: 43 common variable immunodeficiency (CVI), two hyper IgM syndrome (HIM), two IgG subclass deficiency, four ataxia-telangiectasia (AT), and seven X-linked agammaglobulinaemia (XLA). While the assessment of serum specific HCV antibodies in some of these patients was not informative because of the impairment in specific antibody production, the reverse transcriptase polymerase chain reaction (RT-PCR) assay used to detect serum HCV RNA was a useful method for diagnosing infection. We found that 38% of late onset hypogammaglobulinaemic patients (CVI, HIM or IgG subclass deficiency) had evidence of HCV infection. HCV infection was not detectable in patients with XLA or AT. The majority of our patients had persistent viraemia, and those who underwent liver biopsy showed histological findings of chronic hepatitis. Moreover, we could demonstrate in vitro that eight of 18 HCV-infected patients were actively producing anti-HCV antibodies, despite their impaired antibody production. The high rate of HCV infection in hypogammaglobulinaemic patients could be related to several nosocomial routes of transmission, including intravenous immune globulin administration. Despite the persistent viremia only two patients had cirrhosis and none had hepatocarcinoma.

Intranasal immunotherapy with Dermatophagoides extract: in vivo and in vitro results of a double-blind placebo-controlled trial

Intranasal immunotherapy (IT) has been proposed as a means to induce an effective immunity of the nasal mucosa in patients with allergic rhinitis, avoiding systemic side effects. In the present study 20 individuals with chronic allergic rhinitis, and skin prick test reactive to Dermatophagoides pteronyssinus (DP) only, were randomized and subjected to a three months' double-blind placebo-controlled trial of intranasal IT with DP extract. All patients received also sodium cromoglycate as pre-medication. Before and at the end of the treatment the patients performed specific nasal provocation tests, and samples of serum and nasal secretions were collected to measure total and specific IgE, levels of eosinophil cationic protein (ECP), and mast-cell-derived tryptase. A clinical score was computed by the symptoms indicated by the patients. The clinical score did not change in the two groups after the treatment, whereas a decrease in nasal reactivity was observed. Total IgE increased only in secretions from placebo-treated patients, but were not modified in sera. IgE to DP in sera and nasal secretions did not change significantly. Tryptase levels in nasal secretions decreased in both groups, while ECP was unchanged after IT. Serum ECP levels decreased more in actively treated patients than in the placebo group. The data suggest that changes of IgE and inflammatory mediators may be affected by the use of sodium cromoglycate in both groups, but some parameters change early in different directions in IT- and placebo-treated groups.

Immunodeficiency with hyperimmunoglobulinemia M in two female patients is not associated with abnormalities of CD40 or CD40 ligand expression

The immunologic defect in X-linked immunodeficiency and hyperimmunoglobulinemia M (HIM) are related to defective expression of the CD40 ligand (CD40L). We have studied two female patients with HIM to evaluate the role of CD40/CD40L in the pathogenesis of impaired immunoglobulin switching. In addition to recurrent infections characteristic of humoral immunodeficiencies, the two patients had chronic hepatitis caused by type C virus. Phenotypic characterization of peripheral blood mononuclear cells showed a similar picture in both patients, with a reduction in the absolute numbers of CD4 cells and increased numbers of CD8 and CD3/DR cells. B cells (CD19+) were reduced in one patient, but CD40 was expressed on all CD19+ cells in both patients. The expression of CD40L was normal on peripheral blood mononuclear cells from the two patients with HIM on both resting and stimulated cells. The combination of anti-CD40 and cytokines (interleukin-2, interleukin-4, and interleukin-10) was able to restore proliferative capacity to anti-IgM. Peripheral blood mononuclear cells from the two patients with HIM showed a high spontaneous production of IgM in vitro and no production of IgG or IgE. Our data suggest that the defect of isotype switching in female patients with HIM is not related to defective expression of the CD40/CD40L receptor system. A possible role for chronic hepatitis C virus infection in the pathogenesis of the disease is suggested by the detection of specific production of anti-hepatitis C virus IgM.