Increased serum and salivary immunoglobulins against Candida albicans in HIV-infected patients with oral candidiasis

The Role of B-Cells and Antibodies against Candida Vaccine Antigens in Invasive Candidiasis

Systemic candidiasis is an invasive fungal infection caused by members of the genus Candida. The recent emergence of antifungal drug resistance and increased incidences of infections caused by non-albicans Candida species merit the need for developing immune therapies against Candida infections. Although the role of cellular immune responses in anti-Candida immunity is well established, less is known about the role of humoral immunity against systemic candidiasis. This review summarizes currently available information on humoral immune responses induced by several promising Candida vaccine candidates, which have been identified in the past few decades. The protective antibody and B-cell responses generated by polysaccharide antigens such as mannan, β-glucan, and laminarin, as well as protein antigens like agglutinin-like sequence gene (Als3), secreted aspartyl proteinase (Sap2), heat shock protein (Hsp90), hyphally-regulated protein (Hyr1), hyphal wall protein (Hwp1), enolase (Eno), phospholipase (PLB), pyruvate kinase (Pk), fructose bisphosphate aldolase (Fba1), superoxide dismutase gene (Sod5) and malate dehydrogenase (Mdh1), are outlined. As per studies reviewed, antibodies induced in response to leading Candida vaccine candidates contribute to protection against systemic candidiasis by utilizing a variety of mechanisms such as opsonization, complement fixation, neutralization, biofilm inhibition, direct candidacidal activity, etc. The contributions of B-cells in controlling fungal infections are also discussed. Promising results using anti-Candida monoclonal antibodies for passive antibody therapy reinforces the need for developing antibody-based therapeutics including anti-idiotypic antibodies, single-chain variable fragments, peptide mimotopes, and antibody-derived peptides. Future research involving combinatorial immunotherapies using humanized monoclonal antibodies along with antifungal drugs/cytokines may prove beneficial for treating invasive fungal infections.

Effects of Candida albicans infection on defense effector secretion by human oral mucosal epithelial cells

OBJECTIVE

The aim of this study was to investigate the effects of Candida albicans on the production of defense effector molecules by human oral mucosal epithelial cells in vitro.

DESIGN

Immortalized human oral mucosal epithelial (Leuk-1) cells and C. albicans strain 5314 were cocultured at different cell-to-C. albicans ratios. The viability of Leuk-1 cells was determined by MTT and RTCA measurements. The secretory levels of multiple defense effector molecules were determined by Enzyme-linked immunosorbent assay (ELISA).

RESULTS

Our results indicated that C. albicans significantly decreased the secretion of IgG, cystatin C, lactoferrin, and TGF-β1 in a dose-dependent manner and remarkably reduced the production of IgA independent of the cell-to-C. albicans ratio. However, C. albicans clearly enhanced the secretion of IgM, galectin-3, P-selectin, granzyme B and perforin.

CONCLUSION

These results suggest that C. albicans may exert a regulatory role in the defense response of oral mucosal epithelial cells by altering secretory levels of defense effector molecules.

Infection Transmission by Saliva and the Paradoxical Protective Role of Saliva

Saliva is produced by both major (parotid and submandibular and sublingual) and minor (located in the mouth) glands, with different constituents and properties between the two groups. In the mouth saliva is a colorless, odorless, tasteless, watery liquid containing 99% water and 1% organic and inorganic substances and dissolved gases, mainly oxygen and carbon dioxide. Salivary constituents can be grouped into proteins (e.g., amylase and lysozyme), organic molecules (e.g., urea, lipids, and glucose mainly), and electrolytes (e.g., sodium, calcium, chlorine, and phosphates). Cellular elements such as epithelial cells, leukocytes and various hormones, and vitamins have also been detected. The composition of saliva is modified, depending on factors such as secreted amount, circadian rhythm, duration and nature of stimuli, diet, and medication intake, among others.

The Host Cytokine Responses and Protective Immunity in Oropharyngeal Candidiasis

Over the last three decades, the prevalence of oropharyngeal fungal infections has increased enormously, mainly due to an increasing population of immunocompromised patients, including individuals with HIV infection, transplant recipients, and patients receiving cancer therapy. The vast majority of these infections are caused by Candida species. The presence of cytokines in infected tissues ultimately dictates the host defense processes that are specific to each pathogenic organism. During oral infection with Candida, a large number of pro-inflammatory and immunoregulatory cytokines are generated in the oral mucosa. The main sources of these cytokines are oral epithelial cells, which maintain a central role in the protection against fungal organisms. These cytokines may drive the chemotaxis and effector functions of innate and/or adaptive effector cells, such as infiltrating neutrophils and T-cells in immunocompetent hosts, and CD8+ T-cells in HIV+ hosts. Epithelial cells also have direct anti- Candida activity. Several studies have provided a potential link between lower levels of certain pro-inflammatory cytokines and susceptibility to oral C. albicans infection, suggesting that such cytokines may be involved in immune protection. The exact role of these cytokines in immune protection against oropharyngeal candidiasis is still incompletely understood and requires further investigation. Identification of such cytokines with the ability to enhance anti-fungal activities of immune effector cells may have therapeutic implications in the treatment of this oral infection in the severely immunocompromised host.

Levels of salivary IgA antibodies to Candida spp. in HIV-infected adult patients: a systematic review

OBJECTIVE

To perform a systematic review of published data with the aim of evaluating the levels of IgA antibodies to Candida albicans in HIV-infected adult patients.

METHODS

The search strategy was based on PubMed, Web of Science, Google Scholar, Cochrane and EMBASE databases. Also, the reference lists of included studies were searched. All abstracts found by electronic searches were independently scrutinized by two reviewers. To be eligible for review, the controlled studies had to present the following characteristics: samples of both HIV-infected adults and noninfected adults; appropriate HIV-diagnostic tests for both patient groups (case and control); IgA-diagnostic test applied to a similar population sample.

RESULTS

Of 144 studies found, only six met the initial eligibility criteria, but three were excluded after a thorough analysis. To assess the methodological quality of the three remaining studies, they were categorized according the risk of bias. The three selected studies revealed that the levels of C. albicans-specific IgA antibody were higher in HIV-infected individuals compared with the control group.

CONCLUSION

Adequate IgA antibody responses to C. albicans appear to be maintained, since the levels of these antibodies were higher in all studies selected. Although the findings of this systematic review are encouraging, the scientific evidence should be interpreted carefully because there are only a few reports in the literature, mostly because of the lack of important methodological details or the varying methodologies employed.

Associations among the use of highly active antiretroviral therapy, oral candidiasis, oral Candida species and salivary immunoglobulin A in HIV-infected children

OBJECTIVES

The aim was to examine the impact of antiretroviral therapy on the prevalence of oral candidiasis, recovery of oral Candida spp. , and salivary levels of total secretory immunoglobulin A (SIgA) and Candida-specific SIgA in human immunodeficiency virus (HIV)-infected children.

STUDY DESIGN

Sixty-six HIV+ and 40 HIV- children were cross-sectionally examined for the presence of oral lesions. Whole stimulated saliva samples were collected for the identification of Candida spp. using culture and measurement of total and specific SIgA using enzyme-linked immunosorbent assay (ELISA).

RESULTS

The HIV+ children had a higher prevalence of oral candidiasis (P < .05), higher frequency of detection of Candida spp. (P < .05), and higher levels of total (P < .05) and Candida-specific SIgA (P < .001) than the HIV- children. Among the HIV+ subjects, antiretroviral users had lower viral loads (P < .001) and lower levels of Candida spp. (P < .05) and total SIgA (P < .05) compared with antiretroviral nonusers.

CONCLUSIONS

The use of antiretroviral therapy was associated with decreases in the prevalence of oral candidiasis. This diminished exposure to Candida spp. was accompanied by decreases in levels of total and Candida-specific SIgA.

Salivary microbiota of HIV-positive children and its correlation with HIV status, oral diseases, and total secretory IgA

AIM

This study aimed to investigate the prevalence and levels of salivary microorganisms in HIV-positive children, and their correlation to HIV status, oral lesions, and salivary IgA levels.

DESIGN

Forty-two HIV-positive and 36 control children were clinically examined, had their saliva collected and processed for the microbiological analysis of 38 bacterial taxa by the checkerboard method, and salivary IgA quantification by ELISA.

RESULTS

The majority of the species tested were more prevalent in control children than in the HIV group. Mean concentration of total salivary IgA was similar in both groups. High levels of Veillonella parvula were found in children with cheilitis and herpes. Tannerella forsythia, Eikenella Corrodens, and Propionibacterium acnes were prevalent in children with gingivitis, while Fusobacterium periodonticum, Streptococcus gordonii, and Streptococcus oralis were significantly more frequent in children with no oral lesions. Significant negative correlations between salivary IgA levels and Eubacterium nodatum and oral streptococci were observed (P < 0.05).

CONCLUSION

HIV-seropositive children presented significantly lower prevalence and levels of several bacterial species in saliva; HIV-positive children are able to mount a mucosal immune response; HIV-seropositive children under highly active antiretroviral therapy presented low prevalence of oral lesions.

Salivary IgA to cariogenic bacteria in HIV-positive children and its correlation with caries prevalence and levels of cariogenic microorganisms

The interrelationship of HIV infection, dental caries and mucosal immune responses remains controversial. In our study population of 40 HIV-infected and 40 healthy control children (ages 2-5 years) there was a significantly higher prevalence of dental caries in HIV-infected children (P<0.05). The extent of caries correlated with the severity of HIV disease. To determine whether the immunosuppression that ensues after HIV infection could contribute to the increased caries prevalence, the concentrations of total IgA and IgA specific to cariogenic bacteria (Streptococcus mutans, Streptococcus sobrinus and Lactobacillus acidophilus) were determined in whole saliva by enzyme-linked immunosorbent assay. Levels of the same bacteria were also quantified in saliva using checkerboard DNA-DNA hybridization. A significantly increased level of total salivary IgA was found in the HIV-positive population (P < 0.05), but there were comparable titers of specific IgA to cariogenic bacteria in HIV-positive and healthy controls. The microbiological assessment also demonstrated similar levels of cariogenic microorganisms in both groups. We conclude that HIV-positive children appear to maintain the capacity to mount a mucosal immune response to cariogenic microorganisms, at least until late stages of disease.

Immunopathogenesis of oropharyngeal candidiasis in human immunodeficiency virus infection

Oropharyngeal and esophageal candidiases remain significant causes of morbidity in human immunodeficiency virus (HIV)-infected patients, despite the dramatic ability of antiretroviral therapy to reconstitute immunity. Notable advances have been achieved in understanding, at the molecular level, the relationships between the progression of HIV infection, the acquisition, maintenance, and clonality of oral candidal populations, and the emergence of antifungal resistance. However, the critical immunological defects which are responsible for the onset and maintenance of mucosal candidiasis in patients with HIV infection have not been elucidated. The devastating impact of HIV infection on mucosal Langerhans' cell and CD4(+) cell populations is most probably central to the pathogenesis of mucosal candidiasis in HIV-infected patients. However, these defects may be partly compensated by preserved host defense mechanisms (calprotectin, keratinocytes, CD8(+) T cells, and phagocytes) which, individually or together, may limit Candida albicans proliferation to the superficial mucosa. The availability of CD4C/HIV transgenic mice expressing HIV-1 in immune cells has provided the opportunity to devise a novel model of mucosal candidiasis that closely mimics the clinical and pathological features of candidal infection in human HIV infection. These transgenic mice allow, for the first time, a precise cause-and-effect analysis of the immunopathogenesis of mucosal candidiasis in HIV infection under controlled conditions in a small laboratory animal.

Candida albicans secreted aspartyl proteinases in virulence and pathogenesis

Candida albicans is the most common fungal pathogen of humans and has developed an extensive repertoire of putative virulence mechanisms that allows successful colonization and infection of the host under suitable predisposing conditions. Extracellular proteolytic activity plays a central role in Candida pathogenicity and is produced by a family of 10 secreted aspartyl proteinases (Sap proteins). Although the consequences of proteinase secretion during human infections is not precisely known, in vitro, animal, and human studies have implicated the proteinases in C. albicans virulence in one of the following seven ways: (i) correlation between Sap production in vitro and Candida virulence, (ii) degradation of human proteins and structural analysis in determining Sap substrate specificity, (iii) association of Sap production with other virulence processes of C. albicans, (iv) Sap protein production and Sap immune responses in animal and human infections, (v) SAP gene expression during Candida infections, (vi) modulation of C. albicans virulence by aspartyl proteinase inhibitors, and (vii) the use of SAP-disrupted mutants to analyze C. albicans virulence. Sap proteins fulfill a number of specialized functions during the infective process, which include the simple role of digesting molecules for nutrient acquisition, digesting or distorting host cell membranes to facilitate adhesion and tissue invasion, and digesting cells and molecules of the host immune system to avoid or resist antimicrobial attack by the host. We have critically discussed the data relevant to each of these seven criteria, with specific emphasis on how this proteinase family could contribute to Candida virulence and pathogenesis.

New sensitive method for the measurement of lysozyme and lactoferrin to explore mucosal innate immunity. Part II: time-resolved immunofluorometric assay used in HIV patients with oral candidiasis

The aim of this study was to explore lysozyme and lactoferrin concentrations in human immunodeficiency virus (HIV)-infected patients with oropharyngeal candidiasis (OPC). These proteins were measured by time-resolved immunofluorometric assay, validated in Part I of this study, in paired serum and salivary secretions of 30 patients. Eleven HIV-positive patients without OPC, eight HIV-positive patients with OPC and eleven HIV-negative healthy subjects were included in the study. The relative coefficient of excretion of salivary albumin was used to establish protein origin. In serum, the low lactoferrin concentrations in HIV-infected patients with and without OPC (0.610 mg/l (p < 0.05) and 0.896 mg/l (p < 0.01) vs. 1.439 mg/l in healthy subjects) were probably due to a decrease in nonspecific immunity, particularly the polymorphonuclear cells. In HIV-infected patients with OPC, the high salivary lysozyme and lactoferrin concentrations (170.94 mg/l and 66.48 mg/l vs. 23.35 mg/l and 10.20 mg/l in healthy subjects, respectively) and their mean relative coefficient of excretion of above 1 indicated a high local production of lysozyme and lactoferrin in saliva. The development of OPC in HIV-infected patients could be a consequence of inefficient lysozyme and lactoferrin concentrations and of decreased cooperation between innate and adaptative immune systems.

Nonspecific secretory immunity in HIV-infected patients with oral candidiasis

Buccal and digestive tract opportunistic infections occur frequently in patients infected by HIV. In this study, we measured lysozyme (Lz), lactoferrin (Lf), total IgA (T-IgA), and secretory IgA (S-IgA) levels to investigate nonspecific secretory immunity in HIV-infected patients with oral candidiasis. Serum, saliva, and stool samples were analyzed by time-resolved immunofluorometric assay for Lz and Lf levels and by enzyme-linked immunosorbent assay for T-IgA and S-IgA levels. Mean salivary Lf and T-IgA levels (66.50 mg/L and 0.10 g/L, respectively) and mean fecal Lf, T-IgA, and S-IgA outputs (0.87, 54.0, and 43.6 mg/d, respectively) were significantly higher in HIV-infected patients with oropharyngeal candidiasis than in HIV-infected patients without oropharyngeal candidiasis and healthy subjects. There was a modification in the molecular form rate, with a high increase in S-IgA and monomeric IgA transudation from the plasmatic compartment into salivary and digestive fluids and an increase in salivary Lf local synthesis by polymorphonuclear neutrophils. HIV infection appears to be associated with dysregulation of some of the nonspecific immune factors at the mucosal surface. Despite high saliva concentrations and high intestinal output, innate immunity was not able to stop yeast expansion in HIV-infected patients.