Presence Of Excess Antigen Research Articles

Disseminated cryptococcosis with gastrointestinal involvement and false-negative cryptococcal antigen testing due to postzone phenomenon: a case report and review of the literature

BackgroundCryptococcosis is an increasingly common infection given the growing immunocompromised population worldwide. Cryptococcal antigen (CrAg) testing demonstrates excellent sensitivity and specificity and is the mainstay of diagnosis. However, there may be rare instances in which false-negative CrAg results can delay diagnosis and early treatment, which are critical to ensure positive outcomes.Case presentationA 31-year-old man living with HIV/AIDS who was not taking antiretroviral therapy was hospitalized with fever, diarrhea, and headaches. CD4 count on presentation was 71 cells/uL, and HIV viral load was 3,194,949 copies/mL. Serum CrAg testing was initially negative, however CSF CrAg performed several days later was positive at 1:40 and blood and CSF cultures grew Cryptococcus neoformans. Colonoscopy revealed mucosal papules throughout the sigmoid colon, and tissue biopsy showed yeast within the lamina propria consistent with GI cryptococcosis. Given the high burden of disease, the original serum CrAg specimen was serially diluted and subsequently found to be positive at 1:2,560, confirming the postzone phenomenon.ConclusionCryptococcosis has a wide array of presentations including intraluminal GI disease, as seen in this patient. While serum CrAg testing displays excellent test characteristics, it is important for clinicians to be aware of the rare instances in which false-negative results may occur in the presence of excess antigen, as in this case.

Evaluation of the analytical performance of Roche immunoturbidimetric immunoglobulin assays and comparing to Dade Behring immunonephelometer

Objective: The aim of this study is to evaluate the analytical performance of the Roche immunoturbidimetric immunoglubulin assays, and also compare the results obtained by Roche immunoturbidimetric method to Dade Behring II Nephelometer. Methods: Low and high concentration patient samples and internal quality control materials were used to evaluate precision, limit of detection (LoD) linearity, and sample carry over of Roche immunoturbidimetric analyzer. External quality control results were used to evaluate accuracy. For method comparison, 451 patients serum were analyzed using Roche Hitachi Modular P System with an immunoturbidimetric method and Dade Behring BNII immunonephelometer with an immunonephelometric method. Results: In precision study on Roche immunoturbidimetric immunoglobulin assays, imprecision values were 1.37%, 3.88% and 5.34% for IgG, A and M, respectively. Correlation coefficents between Roche immunoturbidimetric analysis and Dade Behring BN II immunonephelometer were 0.967, 0.979 and 0.939 for IgG, IgA and IgM respectively. Conclusion: In immunoturbidimetric Roche Ig analyses precision for IgG was allowable according to the the desirable quality specifications. However, both IgA and IgM had higher imprecisions than the desirable total precision. Immunoturbidimetric Roche Ig analyses were found linear in the reference values but unreliable results were observed in the presence of excess antigen. The same samples performed on Roche analyzers needed to be diluted suggesting Dade Behring had wider linearity range than Roche immunoturbidimetric analyzer in the presence of excess antigen

Electrospray Ionization–Ion Mobility Spectrometry Identified Monoclonal Antibodies that Bind Exclusively to Either the Monomeric or a Dimeric Form of Prostate Specific Antigen

Macroion mobility spectrometry was used to distinguish between a monoclonal antibody (clone M612165) that bound exclusively to monomeric prostate specific antigen and a different monoclonal antibody (clone M612166) that bound exclusively to a dimeric form of the antigen that only comprised 6.8% of the total protein. In the presence of excess antigen, the mobility spectrum of M612165 was replaced by a composite spectrum that represented a mixture of antibodies that included either one or two equivalents of the protein antigen. In similar circumstances, the mobility spectrum of M612166 was replaced by a composite spectrum that represented a mixture of antibodies that included either two or four equivalents of the protein antigen. When exposed to either of the two antibodies, the mobility spectrum of the prostate specific antigen showed a concomitant decrease in the monomeric antigen in one case and in the dimeric antigen in the other case. While sensitive kinetic exclusion assays demonstrated large differences in the antigen binding behavior of the two antibodies, these functional studies alone were insufficient to reveal the likely structural origins of the observed differences. Macroion mobility measurements were shown to be a useful and informative complement to functional studies in understanding complex macromolecular interactions.

Distinguishing between acute and symptomatic chronic hepatitis B virus infection

Background/Aims: Differentiating between an acute hepatitis B (AH-B) infection and an acute exacerbation of a chronic hepatitis B (CH-B) infection can present a problem for the clinician. The only current serological method of distinguishing between acute and symptomatic chronic hepatitis B virus (HBV) infection is the immunoglobulin M antibody to hepatitis B core antigen (anti-HBc) assay, which can be problematic. Therefore, in an attempt to better distinguish between acute and chronic HBV infection, sera from 26 patients with AH-B and 53 patients with CH-B were compared in a variety of experimental immunoassays. Methods: Experimental assays have been designed to detect free antibody to hepatitis B e antigen (anti-HBe), hepatitis B e antigen (HBeAg)/anti-HBe immune complexes (ICs), and hepatitis B surface antigen (HBsAg)/antibody to hepatitis B surface antigen (anti-HBs) in the presence of excess antigen. An additional assay was developed to detect a novel anti-HBc specificity, designated antibody to woodchuck hepatitis virus (anti-HBcw), which cross-reacts with the core antigen of the woodchuck hepatitis virus. Results: Sera from patients with CH-B showed significantly higher levels of free anti-HBe, HBeAg/anti-HBe ICs, and HBsAg/anti-HBs ICs compared with AH-B patient sera. Furthermore, patients with CH-B consistently produced high titer anti-HBcw, whereas patients with AH-B produced little or no anti-HBcw antibody. Conclusions: The serology of AH-B infection and symptomatic CH-B infection can be distinguished using a variety of experimental immunoassays in addition to the immunoglobulin M anti-HBc assay.

Contribution of the Complement System to Antibody-Mediated Binding of Trypanosoma gambiense to Macrophages

The role of complement in the process of binding of trypanosomes to macrophages in the presence of specific antibody was studied. The aggregation of trypanosomes observed at the optimal antigen-antibody ratio or in the presence of excess antigen inhibited the binding. Complement caused clumped trypanosomes to dissociate, and the free trypanosomes, which were presumed to be coated with antibody that had fixed complement, readily attached to surfaces of phagocytes. Thus, complement was shown to contribute at the site of the antigen-antibody reaction to the creation of an environment suitable for the binding. It seems likely that the trypanosomes dissociated by complement adhered to C3 receptors of the macrophage. However, in the absence of complement and in regions of antibody excess, free trypanosomes also attached to phagocytes. Thus phagocytes may also have receptors for the Fc portion of aggregated antibody. Complement activated by the alternate pathway also enhanced attachment of trypanosomes to phagocytes, but the effect was not as rapid as it was when complement was activated by classical means.

Modulation of Ia-like antigen expression and antigen-presenting activity of human monocytes by endotoxin and zymosan A.

The environmental agents E. coli endotoxin and zymosan A modulated antigen-specific T cell proliferation in vitro, assessed by 3H-TdR uptake. In the continual presence of these agents, human mononuclear leukocyte responses to the antigens tuberculin PPD, Candida albicans, and mumps were significantly reduced. Treatment of adherent cell-depleted T cells with the agents did not affect their subsequent reactivity to soluble antigens in the presence of normal M phi. However, cultures consisting of pretreated M phi, normal T cells, and soluble antigen gave responses that were only 7 to 38% of control values, indicating that the function of the antigen-presenting cell, not the T cell, was inhibited. This effect was observed only when treatment with endotoxin or zymosan A preceded antigen stimulation by at least 24 hr, suggesting that a gradual inhibition of antigen presentation had occurred. When various ratios of normal antigen-pulsed and agent-treated M phi were cultured with normal T cells, antigen-specific responses were not significantly different from control cultures; this indicated that M phi-mediated suppression was not involved. It did not appear that the inhibition was due to enhanced antigen degradation by the treated M phi because responses were not reconstituted in the presence of excess antigen. After endotoxin or zymosan A treatment of the M phi population the proportion of Ia+ cells was reduced significantly, and surface expression of Ia antigen correlated with the ability of the cell population to present antigens to immune T cells. This suggested that endotoxin and zymosan A induce a loss of surface Ia antigen on antigen-presenting cells that inhibits immune T cell activation.

Glomerular Involvement in Human Kala-Azar

Glomerular involvement characterized by mesangial cell proliferation with fibrillar thickening of the axial region and deposits of immune complexes is reported in three human cases of kala-azar. IgG was seen in all 3 and Igm in 2 patients. Complement (C3) was detected in the glomeruli in all cases and fibrinogen in the only case in which it was tested for. The deposits appeared mainly along the mesangium and their staining was particularly strong for complement and IgG. Electron microscopy detected granular electron dense deposits mainly close to mesangial cells. In one case clumps made us of electron dense lamellae were seen in the glomerular basal membrane interpreted as evidence of focal membranolysis. No granulocytes were seen in the glomeruli. Attempts to demonstrate antigen were unsuccessful. The pattern of the lesion resembles that described in the kidney of human cases of hepatosplenic schistosomiasis, and the distribution of the deposits suggests that relatively large, poorly soluble complexes formed either in the presence of excess antigen or, under certain circumstances, in the presence of excess antibody, are trapped in the glomerular capillaries. The aggregates are partially shunted to the mesangial cells, which enlarge and proliferate.

Allogeneic Bone Marrow Transplantation in Irradiated Baboons and Monkeys

Allogeneic hemopoietic cells given to the irradiated baboon or Macaca monkey transform by way of typical hyperbasophilic forms to lymphoid cells which cause a fatal acute secondary disease. This is characterized by an especially rapid course in the baboon, Papio hymadryas. Morphological studies revealed the similarity of these cells to cellular elements which occur in reactions of transplantation immunity. The lymphoid cells undergo rapid degeneration, apparently with allergic death of immunologically competent cells in the presence of excess antigen. Preliminary thymectomy considerably mitigated the course of acute secondary disease in monkeys and facilitated regeneration of donor-type hemopoiesis. It is, therefore, possible that hemopoietic stem cells may take part, along with more mature immunologically competent cells, in the production of an acute reaction or graft-versus-host type. Poor bone marrow repopulation in primates with xenogeneic transplants was seen. Multiple chromosome aberrations were fo...

Detection of Immune Response Against Synthetic Polymers of Amino Acids Employing the Plaque-Forming Cell System

Abstract Incorporation of homologous polypeptide (10-5 M) into plaque assay plates containing anti-GLA30 (LLL) immune lymph node cells specifically inhibited these PFC. However, at lower levels of antigen incorporation an enhancement of PFC was noted. The enhancement was complement-dependent, did not occur with non-immune lymph node cells and was inhibited by specific anti-allotype serum. Cross-reaction studies suggested that the polypeptide did not enhance by merely optimally coating the erythrocytes. Serum titers were measured on modified localized hemolysis-in-gel plates. Titers were increased when certain concentrations of antigen were incorporated into these plates, thereby implicating the increased hemolytic efficiency of complement or antibody in the presence of excess antigen. Puromycin (5 to 25 µg/ml) did not inhibit the production of unenhanced plaques, but prevented the optimal enhancement of plaques by antigen. These same concentrations of puromycin inhibited (40% to 96%, respectively) the incorporation of 14 C-L-leucine into trichloroacetic acid precipitable protein. The inclusion of polypeptide in the incubation medium increased the above incorporation by 20% to 170%; puromycin in addition to polypeptide prevented this increase, although the radioactivity was above that obtained when puromycin alone was present. A similar effect was noted with chloramphenicol. The results suggest that enhancement of anti-polypeptide plaques by incorporation of polymer in the medium is a complex phenomenon and is probably due to at least two factors: the increased hemolytic efficiency of immunoglobulin or complement in the presence of excess antigen, and the stimulation of protein synthesis in immune lymph node cells in the presence of excess antigen.

The in vivo formation and fate of antigen-antibody complexes formed by fragments and polypeptide chains of rabbit gamma-G-antibodies.

The in vivo formation and subsequent fate of complexes formed between specific rabbit gammaG-antibody subunits and circulating protein antigens was studied in rabbits and guinea pigs. Subunits obtained from purified antibodies were injected immediately after an injection of antigen, and the elimination from the circulation of either I*-labeled gammaG-subunits or labeled antigen determined. In the absence of antigen, all gammaG-subunits which lack the Fc fragment were rapidly eliminated. In the presence of excess antigen, F (ab')(2), Fab and Fd fragments reacted with antigen and remained in the circulation as complexes which were eliminated at the same rate as the antigen. Fab hybrids containing a specific Fd fragment and a nonspecific L chain similarly reacted with antigen and remained in the circulation complexed to antigen. In contrast, L chains and Fab hybrids containing a specific L chain and a nonspecific Fd fragment did not react with antigen in vivo and were rapidly eliminated in both presence and absence of antigen. H chains remained in the circulation of rabbits in the absence of antigen, however, in the presence of antigen, more H chains which formed complexes with antigen remained in the intravascular space and were rapidly eliminated when the immune elimination of the antigen by the host occurred. Nonspecific H chains were rapidly eliminated from the circulaion of guinea pigs, whereas specific H chains remained in the circulation with the antigen. F (ab')(2) fragments formed complexes with antigen near antibody equivalence and in antibody excess which were rapidly eliminated, however, less effectively than complexes formed near antibody equivalence with intact gammaG. Complexes formed in antibody excess between Fab fragments and H chains remained in the circulation at all concentrations studied and were eliminated at the rate of antigen. The role of the Fc fragment in the immune elimination of antigen-antibody complexes is discussed.