Adel Almogren

Cancer vaccines and carbohydrate epitopes.

Tumor-associated carbohydrate antigens (TACA) result from the aberrant glycosylation that is seen with transformation to a tumor cell. The carbohydrate antigens that have been found to be tumor-associated include the mucin related Tn, Sialyl Tn, and Thomsen-Friedenreich antigens, the blood group Lewis related Lewis(Y), Sialyl Lewis(X) and Sialyl Lewis(A), and Lewis(X) (also known as stage-specific embryonic antigen-1, SSEA-1), the glycosphingolipids Globo H and stage-specific embryonic antigen-3 (SSEA-3), the sialic acid containing glycosphingolipids, the gangliosides GD2, GD3, GM2, fucosyl GM1, and Neu5GcGM3, and polysialic acid. Recent developments have furthered our understanding of the T-independent type II response that is seen in response to carbohydrate antigens. The selection of a vaccine target antigen is based on not only the presence of the antigen in a variety of tumor tissues but also on the role this antigen plays in tumor growth and metastasis. These roles for TACAs are being elucidated. Newly acquired knowledge in understanding the T-independent immune response and in understanding the key roles that carbohydrates play in metastasis are being applied in attempts to develop an effective vaccine response to TACAs. The role of each of the above mentioned carbohydrate antigens in cancer growth and metastasis and vaccine attempts using these antigens will be described.

The nonplanar secretory IgA2 and near planar secretory IgA1 solution structures rationalize their different mucosal immune responses.

Secretory IgA (SIgA) is the most prevalent human antibody and is central to mucosal immunity. It exists as two subclasses, SIgA1 and SIgA2, where SIgA2 has a shorter hinge joining the Fab and Fc regions. Both forms of SIgA are predominantly dimeric and contain an additional protein called the secretory component (SC) that is attached during the secretory process and is believed to protect SIgA in harsh mucosal conditions. Here we locate the five SC domains relative to dimeric IgA2 within SIgA2 using constrained scattering modeling. The x-ray and sedimentation parameters showed that SIgA2 has an extended solution structure. The constrained modeling of SIgA2 was initiated using two IgA2 monomers that were positioned according to our best fit solution structure for dimeric IgA1. SC was best located along the convex edge of the Fc-Fc region. The best fit models showed that SIgA2 is significantly nonplanar in its structure, in distinction to our previous near planar SIgA1 structure. Both the shorter IgA2 hinges and the presence of SC appear to displace the four Fab regions out of the Fc plane in SIgA2. This may explain the noncovalent binding of SC in some SIgA2 molecules. This nonplanar structure is predicted to result in specific immune properties for SIgA2 and SIgA1. It may explain differences observed between the SIgA1 and SIgA2 subclasses in terms of their interactions with antigens, susceptibility to proteases, effects on receptors, and distribution in different tissues. The different structures account for the prevalence of both forms in mucosal secretions.

Location of secretory component on the Fc edge of dimeric IgA1 reveals insight into the role of secretory IgA1 in mucosal immunity.

Secretory immunoglobulin A (SIgA) is the most prevalent antibody in the human body and a first line of defense in mucosal immunity. We located secretory component (SC) relative to dimeric IgA1 (dIgA1) within the SIgA1 structure using the constrained modeling of solution scattering and analytical ultracentrifugation data. The extended solution structure of dIgA1 is largely preserved within SIgA1. From conformational searches of SC locations, the best-fit SC models within SIgA1 show that SC is extended along the outermost convex edge of the Fc dimer in dIgA1. The topology of our SIgA1 structure reveals that it is able to bind to one FcαRI receptor molecule. SC binding to the Fc dimer confers protection to SIgA1 by the masking of proteolytically susceptible surface sites from bacterial proteases in the harsh environment of the mucosa. The models support a “zipper-like” unfolding of SC upon dIgA1 in the formation and transportation of SIgA1 into the mucosa.

Implications of the Near-Planar Solution Structure of Human Myeloma Dimeric IgA1 for Mucosal Immunity and IgA Nephropathy

IgA is unique in being able to form a diverse range of polymeric structures. Increases in the levels of dimeric IgA1 (dIgA1) in serum have been implicated in diseases such as IgA nephropathy. We have determined the solution structure for dIgA1 by synchrotron x-ray and neutron scattering and analytical ultracentrifugation. The Guinier radius of gyration (RG) of 7.60–8.65 nm indicated that the two monomers within dIgA1 are arranged in an extended conformation. The distance distribution curve P(r) gave an overall length (L) of 22–26 nm. These results were confirmed by the sedimentation coefficient and frictional ratio of dIgA1. Constrained scattering modeling starting from the IgA1 monomer solution structure revealed a near-planar dimer structure for dIgA1. The two Fc regions form a slightly bent arrangement in which they form end-to-end contacts, and the J chain was located at this interface. This structure was refined by optimizing the position of the four Fab regions. From this, the best-fit solution structures show that the four Fab Ag-binding sites are independent of one another, and the two Fc regions are accessible to receptor binding. This arrangement allows dIgA1 to initiate specific immune responses by binding to FcαRI receptors, while still retaining Ag-binding ability, and to be selectively transported to mucosal surfaces by binding to the polymeric Ig receptor to form secretory IgA. A mechanism for the involvement of dIgA1 oligomers in the pathology of IgA nephropathy is discussed in the light of this near-planar structure.

Structural and Functional Consequences of Cleavage of Human Secretory and Human Serum Immunoglobulin A1 by Proteinases from Proteus mirabilis and Neisseria meningitidis

ABSTRACT The cleavage of human serum monomeric immunoglobulin A1 (IgA1) and human secretory IgA1 (S-IgA1) by IgA1 proteinase of Neisseriameningitidis and cleavage by the proteinase from Proteusmirabilis have been compared. For serum IgA1, both proteinases cleaved only the α chain. N. meningitidis proteinase cleaved only in the hinge. P. mirabilis proteinase sequentially removed the tailpiece, the CH3 domain, and the CH2 domain. The cleavage of S-IgA1 by N. meningitidis proteinase occurred only in the hinge and was as rapid as that of serum IgA1. P. mirabilis proteinase predominantly cleaved the secretory component (SC) of S-IgA1. The SC of S-IgA1, whether cleaved or not, appeared to protect the α1 chain. Purified Fc fragment derived from the cleavage of serum IgA1 by N. meningitidis proteinase stimulated a respiratory burst in neutrophils through Fcα receptors, whereas the (Fcα1)2-SC fragment from digested S-IgA1 did not. The loss of the tailpiece from serum IgA1 treated with P. mirabilis proteinase had little effect, but the loss of the CH3 domain was concurrent with a rapid loss in the ability to bind to Fcα receptors. S-IgA1 treated with P. mirabilis proteinase under the same conditions retained the ability to bind to Fcα receptors. The results are consistent with the Fcα receptor binding site being at the CH2-CH3 interface. These data shed further light on the structure of S-IgA1 and indicate that the binding site for the Fcα receptor in S-IgA is protected by SC, thus prolonging its ability to activate phagocytic cells at the mucosal surface.

A comparison of the binding of secretory component to immunoglobulin A (IgA) in human colostral S-IgA1 and S-IgA2.

A detailed investigation of the binding of secretory component to immunoglobulin A (IgA) in human secretory IgA2 (S‐IgA2) was made possible by the development of a new method of purifying S‐IgA1, S‐IgA2 and free secretory component from human colostrum using thiophilic gel chromatography and chromatography on Jacalin‐agarose. Sodium dodecyl sulphate–polyacrylamide gel electrophoresis of unreduced pure S‐IgA2 revealed that, unlike in S‐IgA1, a significant proportion of the secretory component was bound non‐covalently in S‐IgA2. When S‐IgA1 was incubated with a protease purified from Proteus mirabilis the secretory component, but not the α‐chain, was cleaved. This is in contrast to serum IgA1, in which the α‐chain was cleaved under the same conditions – direct evidence that secretory component does protect the α‐chain from proteolytic cleavage in S‐IgA. Comparisons between the products of cleavage with P. mirabilis protease of free secretory component and bound secretory component in S‐IgA1 and S‐IgA2 also indicated that, contrary to the general assumption, the binding of secretory component to IgA is different in S‐IgA2 from that in S‐IgA1.

Antenatal screening for Toxoplasma gondii infection at a tertiary care hospital in Riyadh, Saudi Arabia.

Background and Objectives : Congenital toxoplasmosis is associated with significant morbidity and mortality. This study investigates the prevalence of toxoplasmosis among pregnant women. Design and Setting : A retrospective study at King Khalid University Hospital, Riyadh from September 2009 to August 2010. Patients and Methods:0 Laboratory data of 2176 pregnant women screened for Toxoplasma gondii in the antenatal care unit were assessed during the study period. The mean (SD) age of the women and the duration of pregnancy were 25 (7.3) years and 18 (7.7) weeks, respectively. Data were extracted for the presence or absence of anti-T gondii immunoglobulin G (IgG) and IgM antibodies. Results : Of 2176 sera tested, 1351 (62%) did not show any evidence of exposure to T gondii. The remaining 825 (38%) samples tested positive for anti-T gondii IgG antibodies, and none was found to have anti-T gondii IgM antibodies in the serum. These data reveal that a significantly high number of women in the antenatal care unit at King Khalid University Hospital in Riyadh had been exposed to T gondii. Conclusion : A high prevalence of toxoplasmosis among pregnant women warrants multicenter community-based investigations for assessment of T gondii infection and identification of risk factors for transmission of toxoplasmosis in general, and particularly during pregnancy.

Q fever: a neglected zoonosis in Saudi Arabia

BACKGROUND AND OBJECTIVES Infection due to Coxiella burnetii (C burnetii), the causative agent of Q fever is rarely sought for in clinical practice. This study was performed to detect C burnetii infection in patients with pyrexia of undetermined cause (PUC). DESIGN AND SETTINGS This is a prospective study conducted at King Khalid University Hospital, Riyadh between March 2011 and January 2013. PATIENTS AND METHODS A total of 3 mL venous blood was collected from 51 patients with PUC at King Khalid University Hospital, Riyadh. This group of patients included 30 males and 21 females (mean age 33.9 [21.3] years) with the history of febrile illness ranging between 4 and 8 weeks. A control group of 50 healthy individuals comprising 39 males and 11 females (mean age 27 [9] years) was also included in the study. Detection of phase II C burnetii–specific IgG antibodies was performed by immunofluorescence assay, and a titer of >1:64 was considered positive. RESULTS Phase II C burnetii–specific IgG antibodies were detected in 18 (35.2%) patients out of the total 51 tested. Two (4%) individuals out of 50 in the control group tested positive for anti–C burnetii IgG antibodies. The proportion of positive results among the patients was significantly higher than the controls (P<.0002, 95% CI, 15.09–46.25). The antibody titer range was between 1:128 and 1:1024 where 6 patients had titers of 1:256, 5 had 1:512, 4 had 1024, and 3 had 1:128. CONCLUSION The evidence of C burnetii infection in a sizable number of patients emphasizes the need for inclusion of serologic investigations for Q fever in patients with PUC.

Garlic and onion sensitization among Saudi patients screened for food allergy: a hospital based study

BACKGROUND Detection of specific IgE antibodies against food materials indicates allergic sensitization. Some very widely consumed foods materials such as garlic and onion have rarely been investigated for their allergenic potential. OBJECTIVES To assess the presence of garlic and onion specific IgE antibodies in patients investigated for food allergy. METHODS Radioallergosorbent test (RAST) results of 108 patients with clinical suspicion of food allergy who were specifically screened for garlic and onion specific IgE antibodies along with other food allergens were analyzed retrospectively at King Khalid University Hospital between January 2008 and April 2009. This group of patients included 73 males and 35 females with mean age 27+13.2 years. Estimation of garlic and onion specific IgE antibodies was performed by radioallergosorbent test (RAST) using Pharmacia ImmunoCAP 250 analyzer. RESULTS Out of the 108 patients 15 (13.8%) had garlic and onion specific IgE antibodies in their sera. Garlic specific IgE antibodies with the RAST scores between one to four were present in 14 and onion specific IgE were detected in 13 patients. For garlic specific IgEs majority of patients (08) had RAST score of one (0.35-0.69 kU/L) and for onion specific IgE antibodies seven patients had RAST score of two (0.70-3.49 kU/L). Among these patients 12 (80%) were found to have coexisting specific IgE antibodies against garlic and onion. CONCLUSION The presence of garlic and onion specific IgE antibodies in a sizeable number of patients indicate sensitization and allergenic potential of these food materials.

Screening for hen's egg and chicken meat specific IgE antibodies in Saudi patients with allergic disorders.

BACKGROUND Allergy to hens egg and meat contributes significantly to the manifestations of food allergy all over the world. OBJECTIVES This study was performed to assess the presence of hens egg and meat specific IgE antibodies among patients investigated for various allergic disorders. METHODS This is a retrospective study performed at King Khalid University Hosptial, Riyadh. Data from 421 patients with allergic disorders screened for food specific IgE antibodies between January 2009 and March 2011 were analyzed. Sixty (14.25%) patients including 42 males and 18 females with the mean age (sd) of 7.5 (7.4) years were found to have specific IgE antibodies against hens egg and chicken meat. There were 56 (93.3%) children and 4 (6.7%) adult patients. Specific IgE antibodies were measured by radioallergosorbent test (RAST) using Pharmacia ImmunoCAP 250 analyzer. RESULTS Atopic dermatitis was the most common (55%) clinical condition. Out of the total 60 patients harboring hens egg and chicken meat specific IgE antibodies high levels of egg white, yolk and chicken meat specific IgEs were detected in 58 (96.6%), 37 (61.6%) and 6 (10%) patients respectively. Both the egg white and yolk antibodies coexisted in 35 (58.3%) patients. CONCLUSION Sensitization against hens egg was higher compared to the chicken meat. Egg white sensitization higher than the egg yolk particularly in Saudi children with food related allergic disorders.