Combined immunomagnetic cell sorting and ELISPOT assay for the phenotypic characterization of specific antibody-forming cells

Detection of allergen-specific antibody-secreting cells in dogs by ELISPOT

Current laboratory tests are unable to distinguish healthy from allergic dogs. Unlike serum antibody responses, circulating antibody-secreting cells (ASC) are temporarily induced after each contact with the antigen. These ASC can be identified using ELISPOT and the observation of allergen-specific ASC might correlate with the causative allergens in dogs with an allergic dermatitis. In this study, blood was sampled from six privately-owned allergic dogs and six non-allergic laboratory beagles to determine the frequency of circulating allergen-specific ASC for common allergens. Blood IgE+, IgA + and IgG + cells were magnetically isolated to determine the number of allergen-specific ASC with ELISPOT for Dermatophagoides farinae, Dermatophagoides pteronyssinus, Alternaria alternata, birch, timothy grass, wheat, cow's milk, bovine, chicken and lamb meat. For IgA and IgG, allergen-specific spots were observed, however for IgE, no spots were detected for any of the allergens. ELISPOT could not differentiate allergic from non-allergic dogs. When the responses to the different allergens were compared, more IgA ASC for D. pteronyssinus were observed compared to some of the other allergens which was statistically significant for the non-allergic dogs and approached significance in the allergic dogs. These findings indicate that ELISPOT can be used to identify circulating allergen-specific IgA- and IgG-secreting cells. The technique did however not detect allergen-specific IgE ASC and was unable to distinguish allergic from non-allergic dogs. Only a small number of studies have studied allergen-specific IgA in dogs. The finding that dogs have higher numbers of D. pteronyssinus-specific IgA ASC points out that apart from IgE and IgG, it might be interesting to include IgA measurements for certain allergens to analyse the complete spectrum of both the protective and pro-allergic antibody responses.

How Can Elispot Add Information to Improve Knowledge on Tropical Diseases?

Elispot has been used as an important tool for detecting immune cells' products and functions and has facilitated the understanding of host-pathogen interaction. Despite the incredible diversity of possibilities, two main approaches have been developed: the immunopathogenesis and diagnosis/prognosis of infectious diseases as well as cancer research. Much has been described on the topics of allergy, autoimmune diseases, and HIV-Aids, however, Elispot can also be applied to other infectious diseases, mainly leishmaniasis, malaria, some viruses, helminths and mycosis usually classified as tropical diseases. The comprehension of the function, concentration and diversity of the immune response in the infectious disease is pointed out as crucial to the development of infection or disease in humans and animals. In this review we will describe the knowledge already obtained using Elispot as a method for accessing the profile of immune response as well as the recent advances in information about host-pathogen interaction in order to better understand the clinical outcome of a group of tropical and neglected diseases.

Circulating Gut-Homing (α4β7+) Plasmablast Responses against Shigella Surface Protein Antigens among Hospitalized Patients with Diarrhea

Developing countries are burdened with Shigella diarrhea. Understanding mucosal immune responses associated with natural Shigella infection is important to identify potential correlates of protection and, as such, to design effective vaccines. We performed a comparative analysis of circulating mucosal plasmablasts producing specific antibodies against highly conserved invasive plasmid antigens (IpaC, IpaD20, and IpaD120) and two recently identified surface protein antigens, pan-Shigella surface protein antigen 1 (PSSP1) and PSSP2, common to all virulent Shigella strains. We examined blood and stool specimens from 37 diarrheal patients admitted to the Infectious Diseases & Beliaghata General Hospital, Kolkata, India. The etiological agent of diarrhea was investigated in stool specimens by microbiological methods and real-time PCR. Gut-homing (α4β7 (+)) antibody-secreting cells (ASCs) were isolated from patient blood by means of combined magnetic cell sorting and two-color enzyme-linked immunosorbent spot (ELISPOT) assay. Overall, 57% (21 of 37) and 65% (24 of 37) of the patients were positive for Shigella infection by microbiological and real-time PCR assays, respectively. The frequency of α4β7 (+) IgG ASC responders against Ipas was higher than that observed against PSSP1 or PSSP2, regardless of the Shigella serotype isolated from these patients. Thus, α4β7 (+) ASC responses to Ipas may be considered an indirect marker of Shigella infection. The apparent weakness of ASC responses to PSSP1 is consistent with the lack of cross-protection induced by natural Shigella infection. The finding that ASC responses to IpaD develop in patients with recent-onset shigellosis indicates that such responses may not be protective or may wane too rapidly and/or be of insufficient magnitude.

Maternal immunity enhances systemic recall immune responses upon oral immunization of piglets with F4 fimbriae

F4 enterotoxigenic Escherichia coli (ETEC) cause diarrhoea and mortality in piglets leading to severe economic losses. Oral immunization of piglets with F4 fimbriae induces a protective intestinal immune response evidenced by an F4-specific serum and intestinal IgA response. However, successful oral immunization of pigs with F4 fimbriae in the presence of maternal immunity has not been demonstrated yet. In the present study we aimed to evaluate the effect of maternal immunity on the induction of a systemic immune response upon oral immunization of piglets. Whereas F4-specific IgG and IgA could be induced by oral immunization of pigs without maternal antibodies and by intramuscular immunization of pigs with maternal antibodies, no such response was seen in the orally immunized animals with maternal antibodies. Since maternal antibodies can mask an antibody response, we also looked by ELIspot assays for circulating F4-specific antibody secreting cells (ASCs). Enumerating the F4-specific ASCs within the circulating peripheral blood mononuclear cells, and the number of F4-specific IgA ASCs within the circulating IgA⁺ B-cells revealed an F4-specific immune response in the orally immunized animals with maternal antibodies. Interestingly, results suggest a more robust IgA booster response by oral immunization of pigs with than without maternal antibodies. These results demonstrate that oral immunization of piglets with F4-specific maternal antibodies is feasible and that these maternal antibodies seem to enhance the secondary systemic immune response. Furthermore, our ELIspot assay on enriched IgA⁺ B-cells could be used as a screening procedure to optimize mucosal immunization protocols in pigs with maternal immunity.

Enzyme-linked immunospot assays for direct ex vivo measurement of vaccine-induced human humoral immune responses in blood

The enzyme-linked immunospot (ELISPOT) assay was originally developed to enumerate antigen-specific antibody-secreting cells (ASCs), and has subsequently been adapted for various applications, including the detection cytokine-secreting cells. Owing to its exceptionally high sensitivity, the ELISPOT has proven to be especially useful for detecting discrete populations of active cells (e.g., antigen-specific cells). Because of its versatility, the ELISPOT assay is used for a wide range of applications, including clonal analyses of immune responses after vaccination or after immunotherapy. Here we describe standard protocols for the detection of human ASCs specific to virtually any vaccine antigen after enrichment of circulating plasmablasts. In addition, a protocol is described for the measurement of mucosal ASC responses after prior immunomagnetic enrichment of mucosally derived blood lymphocytes. The protocols described allow rapid (~6-8 h) detection of specific ASCs in small (1-2 ml) samples of blood and can be performed in resource-poor settings.

Advances in human B cell phenotypic profiling

To advance our understanding and treatment of disease, research immunologists have been called-upon to place more centralized emphasis on impactful human studies. Such endeavors will inevitably require large-scale study execution and data management regulation (“Big Biology”), necessitating standardized and reliable metrics of immune status and function. A well-known example setting this large-scale effort in-motion is identifying correlations between eventual disease outcome and T lymphocyte phenotype in large HIV-patient cohorts using multiparameter flow cytometry. However, infection, immunodeficiency, and autoimmunity are also characterized by correlative and functional contributions of B lymphocytes, which to-date have received much less attention in the human Big Biology enterprise. Here, we review progress in human B cell phenotyping, analysis, and bioinformatics tools that constitute valuable resources for the B cell research community to effectively join in this effort.

Subcellular resolution mapping of endogenous cytokine secretion by nano-plasmonic-resonator sensor array

Local extracellular signaling is central for cellular interactions and organizations. We report a novel sensing technique to interrogate extracellular signaling at the subcellular level. We developed an in situ immunoassay based on giant optical enhancement of a tunable nano-plasmonic-resonator array fabricated by nanoimprint lithography. Our nanoplasmonic device significantly increases the signal-to-noise ratio to enable the first time submicrometer resolution quantitative mapping of endogenous cytokine secretion. Our study shows a markedly high local interleukin-2 (IL-2) concentration within the immediate vicinity of the cell which finally validates a decades-old hypothesis on autocrine physiological concentration and spatial range. This general sensing technique can be applied for a broad range of cellular communication studies to improve our understanding of subcellular signaling and function.

Two novel assays of alloantibody-secreting cells demonstrating resistance to desensitization with IVIG and rATG

Donor-specific alloantibody presents a major barrier to the successful transplantation of kidneys and hearts. However, the study of alloantibody production has been hampered by both an inadequate source of antibody-secreting cells (ASCs) and a paucity of assays to determine their function. We describe two new assays that allow for the determination of the frequency and specificities of allo-ASCs in humans using purified HLA as targets. These assays demonstrated allo-ASCs in the CD138(+) fraction of the bone marrow, but not in peripheral blood. Alloantibody specificities in these assays correlated well with those detected in the serum suggesting that bone marrow-derived ASCs are indeed a major source of alloantibody in vivo. However, ASCs for a specific HLA antigen were rare with an estimated frequency of only 1/2 x 10(6) marrow cells. Pretransplant treatment in vivo with multiple plasmaphereses and low-dose IVIG alone or in combination with rATG had no effect on ASC number or alloantibody production. These techniques allow for the study of allospecific ASCs and provide a method to test the potential efficacy of agents on alloantibody production in vivo.

Maturation and trafficking markers on rotavirus-specific B cells during acute infection and convalescence in children

We have previously studied B cells, from people and mice, that express rotavirus-specific surface immunoglobulin (RV-sIg) by flow cytometry with recombinant virus-like particles that contain green fluorescent protein. In the present study we characterized circulating B cells with RV-sIg in children with acute and convalescent infection. During acute infection, circulating RV-sIgD(-) B cells are predominantly large, CD38(high), CD27(high), CD138(+/-), CCR6(-), alpha4beta7(+), CCR9(+), CCR10(+), cutaneous lymphocyte antigen-negative (CLA(-)), L-selectin(int/-), and sIgM(+), sIgG(-), sIgA(+/-) lymphocytes. This phenotype likely corresponds to gut-targeted plasma cells and plasmablasts. During convalescence the phenotype switches to small and large lymphocytes, CD38(int/-), CD27(int/-), CCR6(+), alpha4beta7(+/-), CCR9(+/-) and CCR10(-), most likely representing RV-specific memory B cells with both gut and systemic trafficking profiles. Of note, during acute RV infection both total and RV-specific murine IgM and IgA antibody-secreting cells migrate efficiently to CCL28 (the CCR10 ligand) and to a lesser extent to CCL25 (the CCR9 ligand). Our results show that CCR10 and CCR9 can be expressed on IgM as well as IgA antibody-secreting cells in response to acute intestinal infection, likely helping target these cells to the gut. However, these intestinal infection-induced plasmablasts lack the CLA homing receptor for skin, consistent with mechanisms of differential CCR10 participation in skin T versus intestinal plasma cell homing. Interestingly, RV memory cells generally lack CCR9 and CCR10 and instead express CCR6, which may enable recruitment to diverse epithelial sites of inflammation.

Intensive treatment for childhood acute lymphoblastic leukemia reduces immune responses to diphtheria, tetanus, and Haemophilus influenzae type b

OBJECTIVES

Immunity to diphtheria toxoid (D), tetanus toxoid (T), and Haemophilus influenzae type b (Hib) is affected in children with acute lymphoblastic leukemia (ALL). The aims were to examine immunity and to compare the response to immunization at 1 or 6 months after treatment.

METHODS

Thirty-one patients were immunized with DT and conjugated Hib vaccine (ActHib) at 1 month or 6 months after treatment of ALL with the NOPHO 92 protocol. Antibody levels were determined before and 3 weeks after vaccination. Specific T and Hib antibody-secreting cells of IgG/IgA/IgM isotypes were analyzed in peripheral blood using an ELISPOT technique.

RESULTS

All specific antibody levels decreased during ALL treatment, and protective levels after treatment were noted for 17% against D, 33% against T, and 100% against Hib. No high-risk patient had full D or T protection after treatment. After vaccination all the standard- and intermediate-risk patients achieved full protection against D, T, and Hib. The high-risk group showed insufficient immune response (full protection after vaccination: D 56%, T 22%, Hib 78%). No difference was found between vaccination at 1 month or 6 months after treatment. The poor antibody production in the high-risk group correlated to low numbers of antibody-secreting cells.

CONCLUSIONS

Nonprotective antibody levels against D, T, and Hib after childhood ALL are more common than previously thought. Insufficient immune response was restricted to the high-risk group and was related to a low number of memory B cells in this study. Immunizations should be included in follow-up after childhood ALL, and the policy should be adapted to treatment intensity.

Rotavirus-specific B cells induced by recent infection in adults and children predominantly express the intestinal homing receptor alpha4beta7

In vivo replication of rotaviruses is generally limited to enterocytes. Because of this restriction, most blood circulating rotavirus-specific B cells are hypothesized to originate in Peyer's patches and should express the intestinal homing receptor alpha4beta7. To test this hypothesis in humans, we used a flow cytometry assay that identifies antigen-activated (IgD-) B cells (CD19+) that express surface rotavirus-specific immunoglobulin. With this assay we could detect rotavirus-specific B cells in both children and adults with an acute rotavirus (RV) infection. Staining with an anti-alpha4beta7 monoclonal antibody, we could determine that B cells that express rotavirus-specific surface immunoglobulin predominantly express alpha4beta7. The response of rotavirus-specific antibody-secreting cells in the peripheral blood of children and adults with acute rotavirus infection was also studied by ELISPOT. The antibody-secreting cells of children were mainly of the IgM isotype, while the antibody-secreting cells of adults were predominantly of the IgA and IgG isotype. alpha4beta7+ and alpha4beta7- subsets of peripheral blood mononuclear cells were purified using paramagnetic beads and then tested in the ELISPOT assay. Rotavirus-specific antibody-secreting cells were predominantly present in the alpha4beta7+ subpopulation. The flow cytometry assay we have described will permit future studies to characterize the phenotype of virus-specific B cells and could be useful in the study of the immunogenicity and protective efficacy of RV vaccines and the identification of markers of protective immunity.

Disturbed peripheral B lymphocyte homeostasis in systemic lupus erythematosus

In patients with active systemic lupus erythematosus (SLE), a marked B lymphocytopenia was identified that affected CD19(+)/CD27(-) naive B cells more than CD19(+)/CD27(+) memory B cells, leading to a relative predominance of CD27-expressing peripheral B cells. CD27(high)/CD38(+)/CD19(dim)/surface Ig(low)/CD20(-)/CD138(+) plasma cells were found at high frequencies in active but not inactive SLE patients. Upon immunosuppressive therapy, CD27(high) plasma cells and naive CD27(-) B cells were markedly decreased in the peripheral blood. Mutational analysis of V gene rearrangements of individual B cells confirmed that CD27(+) B cells coexpressing IgD were memory B cells preferentially using V(H)3 family members with multiple somatic mutations. CD27(high) plasma cells showed a similar degree of somatic hypermutation, but preferentially employed V(H)4 family members. These results indicate that there are profound abnormalities in the various B cell compartments in SLE that respond differently to immunosuppressive therapy.

Advances in cell separation: recent developments in counterflow centrifugal elutriation and continuous flow cell separation

Cell separation by counterflow centrifugal elutriation (CCE) or free flow electrophoresis (FFE) is performed at lower frequency than cell cloning and antibody-dependent, magnetic or fluorescence-activated cell sorting. Nevertheless, numerous recent publications confirmed that these physical cell separation methods that do not include cell labeling or cell transformation steps, may be most useful for some applications. CCE and FFE have proved to be valuable tools, if homogeneous populations of normal healthy untransformed cells are required for answering scientific questions or for clinical transplantation and cells cannot be labeled by antibodies, because suitable antibodies are not available or because antibody binding to a cell surface would induce the cell reaction which should be investigated on purified cells or because antibodies bound to the surface hamper the use of the isolated cells. In addition, the methods are helpful for studying the biological reasons for, or effects of, changes in cell size and cellular negative surface charge density. Although the value of the methods was confirmed in recent years by a considerable number of important scientific results, activities to further develop and improve the instruments have, unfortunately, declined.