Antibody-mediated regulation of the immune response

Antibodies administered in vivo together with the antigen they are specific for can regulate the immune response to that antigen. This phenomenon is called antibody-mediated feedback regulation and has been known for over 100 years. Both passively administered and actively produced antibodies exert immunoregulatory functions. Feedback regulation can be either positive or negative, resulting in >1000-fold enhancement or >99% suppression of the specific antibody response. Usually, the response to the entire antigen is up- or downregulated, regardless of which epitope the regulating antibody recognizes. IgG of all isotypes can suppress responses to large particulate antigens like erythrocytes, a phenomenon used clinically in Rhesus prophylaxis. IgG suppression works in mice lacking the known Fc-gamma receptors (FcgammaR) and a likely mechanism of action is epitope masking. IgG1, IgG2a and IgG2b administered together with soluble protein antigens will enhance antibody and CD4+ T-cell responses via activating FcgammaR, probably via increased antigen presentation by dendritic cells. IgG3 as well as IgM also enhance antibody responses but their effects are dependent on their ability to activate complement. A possible mechanism is increased B-cell activation caused by immune complexes co-crosslinking the B-cell receptor with the complement-receptor 2/CD19 receptor complex, known to lower the threshold for B-cell activation. IgE-antibodies enhance antibody and CD4+ T-cell responses to small soluble proteins. This effect is entirely dependent on the low-affinity receptor for IgE, CD23, the mechanism probably being increased antigen presentation by CD23+ B cells.

IgE Enhances Antibody and T Cell Responses In Vivo via CD23+ B Cells

IgE Abs, passively administered together with their specific Ag, can enhance the production of Abs recognizing this Ag by >100-fold. IgE-mediated feedback enhancement requires the low affinity receptor for IgE, CD23. One possible mechanism is that B cells take up IgE-Ag via CD23 and efficiently present Ag to Th cells, resulting in better Ab responses. To test whether IgE Abs have an effect on Th cells in vivo, mice were adoptively transferred with CD4+ T cells expressing a transgenic OVA-specific TCR, before immunization with IgE anti-TNP (2,4,6-trinitrophenyl) plus OVA-TNP or with OVA-TNP alone. IgE induced a 6- to 21-fold increase in the number of OVA-specific T cells. These cells acquired an activated phenotype and were visible in splenic T cell zones. The T cell response peaked 3 days after immunization and preceded the OVA-specific Ab response by a few days. Transfer of CD23+ B cells to CD23-deficient mice rescued their ability to respond to IgE-Ag. Interestingly, in this situation also CD23-negative B cells produce enhanced levels of OVA-specific Abs. The data are compatible with the Ag presentation model and suggest that B cells can take up Ag via "unspecific" receptors and activate naive T cells in vivo.

Serum proteomic profiling at diagnosis predicts clinical course, and need for intensification of treatment in inflammatory bowel disease

BACKGROUND

Success in personalized medicine in complex disease is critically dependent on biomarker discovery. We profiled serum proteins using a novel proximity extension assay [PEA] to identify diagnostic and prognostic biomarkers in inflammatory bowel disease [IBD].

METHODS

We conducted a prospective case-control study in an inception cohort of 552 patients [328 IBD, 224 non-IBD], profiling proteins recruited across six centres. Treatment escalation was characterized by the need for biological agents or surgery after initial disease remission. Nested leave-one-out cross-validation was used to examine the performance of diagnostic and prognostic proteins.

RESULTS

A total of 66 serum proteins differentiated IBD from symptomatic non-IBD controls, including matrix metallopeptidase-12 [MMP-12; Holm-adjusted p = 4.1 × 10-23] and oncostatin-M [OSM; p = 3.7 × 10-16]. Nine of these proteins are associated with cis-germline variation [59 independent single nucleotide polymorphisms]. Fifteen proteins, all members of tumour necrosis factor-independent pathways including interleukin-1 (IL-1) and OSM, predicted escalation, over a median follow-up of 518 [interquartile range 224-756] days. Nested cross-validation of the entire data set allowed characterization of five-protein models [96% comprising five core proteins ITGAV, EpCAM, IL18, SLAMF7 and IL8], which define a high-risk subgroup in IBD [hazard ratio 3.90, confidence interval: 2.43-6.26], or allowed distinct two- and three-protein models for ulcerative colitis and Crohn's disease respectively.

CONCLUSION

We have characterized a simple oligo-protein panel that has the potential to identify IBD from symptomatic controls and to predict future disease course. Further prospective work is required to validate our findings.

Bright-field microscopy visualization of proteins and protein complexes by in situ proximity ligation with peroxidase detection

BACKGROUND

The in situ proximity ligation assay (PLA) allows a protein or protein complex to be represented as an amplifiable DNA molecule. Recognition is mediated by proximity probes consisting of antibodies coupled with oligonucleotides. Upon dual binding of the proximity probes, the oligonucleotides direct the formation of a circular DNA molecule, which is then amplified by rolling-circle replication. The localized concatemeric product is then detected with fluorescent probes. The in situ PLA enables localized detection of individual native proteins or interacting protein pairs in fixed cells or tissue sections, thus providing an important tool for basic and clinical research.

METHODS

We used horseradish peroxidase (HRP)-conjugated oligonucleotides to couple in situ PLA with enzymatic visualization of the localized detection event.

RESULTS

We demonstrate the detection of protein complexes, both in cells and in tissue sections, and show that we can quantify the complexes with image-analysis software specially developed for recognizing HRP signals in bright-field microscopy images. We show that fluorescence and HRP signals produce equivalent results, both in cultured cells and in tissue samples.

CONCLUSIONS

The combination of in situ PLA with bright-field detection and automated image analysis allows the signals present to be counted in an automated fashion and thus provides a sensitive and specific method for quantification of proteins and protein complexes with bright-field microscopy. With this approach, in situ PLA can be used without the requirement for expensive fluorescence microscopes, thereby avoiding problems with nonspecific fluorescence while maintaining compatibility with conventional histologic staining.

IgE Enhances Specific Antibody and T-cell Responses in Mice Overexpressing CD23

IgE administered with its specific antigen in vivo induces enhanced proliferation of specific T cells as well as enhanced production of specific antibodies. Both effects are dependent on the low-affinity receptor for IgE (CD23) and the underlying mechanism is thought to be increased antigen presentation following uptake of IgE/antigen complexes via CD23(+) B cells. By contrast, CD23 negatively regulates antibody responses to antigens administered with alum, i.e. without IgE. This effect has been observed as low IgG1 and IgE responses in transgenic mice overexpressing CD23 (CD23Tg). The present study was designed to test whether IgE could enhance antibody and T-cell responses in CD23Tg animals or whether CD23's downregulatory effect precludes IgE-mediated enhancement. IgE-anti-TNP administered with OVA-TNP enhances the OVA-specific antibody responses in wild-type (wt) and CD23Tg mice equally well. Interestingly, the total magnitude of antibody responses to IgE + OVA-TNP and to uncomplexed OVA-TNP, as well as to sheep erythrocytes and keyhole limpet haemocyanine, were lower in the CD23Tg mice. IgE induced proliferation of OVA-specific CD4(+) T cells to the same degree in wt and CD23Tg mice. The effect on T cells was dependent on CD23(+) B cells as demonstrated in in vitro proliferation assays. In conclusion, CD23 does indeed have dual immunoregulatory effects in the same animal. The receptor mediates enhancement of antibody and T-cell responses to IgE-complexed antigen, most likely via increased presentation of complexed antigen, while it negatively regulates the total antibody response to a variety of antigens.

Shb deficient mice display an augmented TH2 response in peripheral CD4+ T cells

Background

Shb, a ubiquitously expressed Src homology 2 domain-containing adaptor protein has previously been implicated in the signaling of various tyrosine kinase receptors including the TCR. Shb associates with SLP76, LAT and Vav, all important components in the signaling cascade governing T cell function and development. A Shb knockout mouse was recently generated and the aim of the current study was to address the importance of Shb deficiency on T cell development and function.

Results

Shb knockout mice did not display any major changes in thymocyte development despite an aberrant TCR signaling pattern, including increased basal activation and reduced stimulation-induced phosphorylation. The loss of Shb expression did however affect peripheral CD4+ T_H cells resulting in an increased proliferative response to TCR stimulation and an elevated IL-4 production of naïve T_H cells. This suggests a T_H2 skewing of the Shb knockout immune system, seemingly caused by an altered TCR signaling pattern.

Conclusion

Our results indicate that Shb appears to play an important modulating role on TCR signaling, thus regulating the peripheral CD4+ T_H2 cell response.

IgG3-mediated enhancement of the antibody response is normal in Fc gammaRI-deficient mice

Antibodies, administered together with their specific antigen, can feedback-regulate antibody responses to this antigen. IgG1, IgG2a and IgG2b enhance antibody responses to soluble protein antigens. This effect is primarily mediated by FcRs as enhancement is impaired in FcR gamma-/- mice, reported to lack Fc gammaRI and Fc gammaRIII because of deletion of the common FcR gamma chain. Also IgG3 can enhance antibody responses. However, this effect is unperturbed in FcR gamma-/- mice but severely impaired in complement-depleted animals and in animals lacking complement receptor 1 and 2. Although this argues against involvement of Fc gammaRs, FcR gamma-/- mice may express one-fifth of the normal levels of Fc gammaRI and, in addition, Fc gammaRI has been suggested to bind IgG3. We re-investigated the dependence of IgG3-mediated enhancement on Fc gammaRs using a mouse strain selectively lacking Fc gammaRI and found that IgG3-mediated enhancement is completely normal. Unlike IgE and IgG2a, which are both thought to enhance T-cell proliferation via FcR-mediated antigen presentation, IgG3 was a poor enhancer of T-cell proliferation both in vivo and in vitro. These findings argue against a significant involvement of Fc gammaRs in IgG3-mediated enhancement of antibody responses and support our previous conclusion that complement plays a major role.

Prospective observational study on Stelara (ustekinumab) assessing effectiveness in Crohn's disease (PROSE): a 16-week follow-up

BACKGROUND

Prospectively and systematically collected real-world data on the effectiveness of ustekinumab (anti-interleukin-12/23) for treating Crohn's disease (CD) are still limited.

AIM

To assess the short-term real-world effectiveness of ustekinumab in Swedish patients with active CD.

METHODS

Prospective multicentre study of adult CD patients initiating ustekinumab according to recommended doses at 20 hospitals, between January 2017 and November 2018. Data were collected through an electronic case report form (eCRF) linked to the Swedish Inflammatory Bowel Disease Registry (SWIBREG). The primary outcomes were clinical response (≥3-point-decrease of Harvey-Bradshaw index (HBI)) and remission (HBI ≤4 points) at week 16. Secondary outcomes included C-reactive protein (CRP) and haemoglobin (Hb) at baseline compared to week 16.

RESULTS

Of 114 included patients, 107 (94%) had failed ≥ 1 and 58 (51%) ≥ 2 biological agents (anti-tumour necrosis factor [aTNF] agents or vedolizumab). The 16-week ustekinumab retention rate was 105 (92%). Data on HBI at baseline were available for 96 patients. At week 16, response or remission was achieved in 38/96 (40%) patients (25/96 (26%) achieving clinical remission and 23/96 (24%) showing a clinical response). The median CRP concentration (N = 65) decreased from 6 to 4 mg/l (p = .006). No significant changes in Hb were observed. No incident malignancies or infections, requiring antibiotic treatment, were reported.

CONCLUSIONS

In this nation-wide prospective real-world study of adult patients with CD, ustekinumab was associated with clinical effectiveness when administered according to clinical practice and seemed to represent a safe treatment option.

Frequency and outcomes of treatment dose escalation with biologics in moderate-to-severe psoriasis: a Swedish register study

BACKGROUND

The advent of biosimilars may increase the frequency of dose escalation with biologics in psoriasis.

OBJECTIVE

To explore the frequency and outcomes of dose escalation with adalimumab etanercept, and ustekinumab.

METHODS

Data were extracted from DermaReg-Pso, a psoriasis register in Stockholm, Sweden. The main exposure was treatment, and the main outcome was dose escalation. We describe outcomes with dose escalation by estimating drug survival and changes in the Psoriasis Area and Severity Index (PASI).

RESULTS

554 patients had 946 treatment episodes with adalimumab, etanercept, or ustekinumab. The cumulative incidence of dose escalation was 4.1 per 100 treatment years. The Hazard Ratios (HRs) for dose escalation with ustekinumab vs adalimumab and ustekinumab vs etanercept were 1.93 (95% CI: 1.25-2.98), and 2.20 (95% CI: 1.42-3.41), respectively. After dose escalation, the HRs for treatment discontinuation with adalimumab and etanercept compared with ustekinumab were 3.10 (95% CI: 1.56-6.18) and 7.15 (95% CI: 3.96-12.94), respectively. PASI was higher after compared to before dose escalation for etanercept (p = 0.036), but not for adalimumab (p = 0.832) or ustekinumab (p = 0.300).

CONCLUSIONS

Dose escalation was comparatively more frequent with ustekinumab than with adalimumab or etanercept; however, treatment discontinuation after dose escalation was more common with adalimumab and etanercept than ustekinumab.