Factors That Regulate the Generation of Antibody-Secreting Plasma Cells

Comprehensive antibody and cytokine profiling in hospitalized COVID-19 patients in relation to clinical outcomes in a large Belgian cohort

The immune response in patients with Coronavirus Disease 2019 (COVID-19) is highly variable and is linked to disease severity and mortality. However, antibody and cytokine responses in the early disease stage and their association with disease course and outcome are still not completely understood. In this large, multi-centre cohort study, blood samples of 434 Belgian COVID-19 hospitalized patients with different disease severities (ranging from asymptomatic/mild to critically ill) from the first wave of the COVID-19 pandemic were obtained. Baseline antibody and cytokine responses were characterized and associations with several clinical outcome parameters were determined. Anti-spike immunoglobulin (Ig)G and IgM levels were elevated in patients with a more severe disease course. This increased baseline antibody response however was associated with decreased odds for hospital mortality. Levels of the pro-inflammatory cytokines IL-6, IP-10 and IL-8, the anti-inflammatory cytokine IL-10 and the antiviral cytokines IFN-α, IFN-β and IFN-λ1 were increased with disease severity. Remarkably, we found significantly lower levels of IFN-λ2,3 in critically ill patients compared to patients of the moderate and severe disease category. Finally, levels of IL-8, IL-6, IP-10, IL-10, IFN-α, IFN-β, IFN-γ and IFN-λ1 at baseline were positively associated with mortality, whereas higher IFN-λ2,3 levels were negatively associated with mortality.

A p38α-BLIMP1 signalling pathway is essential for plasma cell differentiation

Plasma cells (PC) are antibody-secreting cells and terminal effectors in humoral responses. PCs differentiate directly from activated B cells in response to T cell-independent (TI) antigens or from germinal center B (GCB) cells in T cell-dependent (TD) antigen-induced humoral responses, both of which pathways are essentially regulated by the transcription factor BLIMP1. The p38 mitogen-activated protein kinase isoforms have already been implicated in B cell development, but the precise role of p38α in B cell differentiation is still largely unknown. Here we show that PC differentiation and antibody responses are severely impaired in mice with B cell-specific deletion of p38α, while B cell development and the GCB cell response are spared. By utilizing a Blimp1 reporter mouse model, we show that p38α-deficiency results in decreased BLIMP1 expression. p38α-driven BLIMP1 up-regulation is required for both TI and TD PCs differentiation. By combining CRISPR/Cas9 screening and other approaches, we identify TCF3, TCF4 and IRF4 as downstream effectors of p38α to control PC differentiation via Blimp1 transcription. This study thus identifies an important signalling pathway underpinning PC differentiation upstream of BLIMP1, and points to a highly specialized and non-redundant role for p38α among p38 isoforms.

B cell memory responses induced by foot-and-mouth disease virus-like particles in BALB/c mice

A challenging but critical question is that new foot-and-mouth disease (FMD) vaccines should be to induce B cell memory to provide antibodies for long-term protection. The maintenance of B cell memory is dependent on long-lived plasma cells (LLPCs) and memory B cells. We developed a chimeric FMDV virus-like particles (FMDV-VLPs), fusing VP1-VP4 into HBcAg. In our study, we investigated if or how long B cell memory was induced by FMDV-VLPs in mice. The data showed that FMDV-VLPs can induce memory humoral responses with a high level of total IgG1, IgG2a, IgA, and FMDV-specific IgG antibodies in serum. The persistence of antibody levels in serum could depend on LLPCs. The proportion of LLPCs in CD19+ cells in bone marrow exhibited a dynamic trend with two peaks at 28 days post-immunization (dpi) and 72 dpi, respectively. Additionally, the proportion of memory B cells in CD19+ cells in the spleen increased significantly both at 7 days post primary immunization and at 7 days post -boost immunization. Of note, LLPCs together with memory B cells contribute to the production of FMDV-specific IgG and IgG1. The changes of LLPCs and memory B cells may be related to TNF-α, IL-6 and, CXCL12. Taken together, FMDV-VLPs could induce B cells memory responses. A further understanding of the mechanisms that FMDV-VLPs how we can manipulate the induction and maintenance of memory B cells and LLPCs will promote vaccine design and likely address several challenges to develop FMDV new vaccines in the future.

Dysregulated Immune Responses in COVID-19 Patients Correlating With Disease Severity and Invasive Oxygen Requirements

The prognosis of severe COVID-19 patients has motivated research communities to uncover mechanisms of SARS-CoV-2 pathogenesis also on a regional level. In this work, we aimed to understand the immunological dynamics of severe COVID-19 patients with different degrees of illness, and upon long-term recovery. We analyzed immune cellular subsets and SARS-CoV-2-specific antibody isotypes of 66 COVID-19 patients admitted to the Hospital Clínico Universidad de Chile, which were categorized according to the WHO ten-point clinical progression score. These included 29 moderate patients (score 4-5) and 37 severe patients under either high flow oxygen nasal cannula (18 patients, score 6), or invasive mechanical ventilation (19 patients, score 7-9), plus 28 convalescent patients and 28 healthy controls. Furthermore, six severe patients that recovered from the disease were longitudinally followed over 300 days. Our data indicate that severe COVID-19 patients display increased frequencies of plasmablasts, activated T cells and SARS-CoV-2-specific antibodies compared to moderate and convalescent patients. Remarkably, within the severe COVID-19 group, patients rapidly progressing into invasive mechanical ventilation show higher frequencies of plasmablasts, monocytes, eosinophils, Th1 cells and SARS-CoV-2-specific IgG than patients under high flow oxygen nasal cannula. These findings demonstrate that severe COVID-19 patients progressing into invasive mechanical ventilation show a distinctive type of immunity. In addition, patients that recover from severe COVID-19 begin to regain normal proportions of immune cells 100 days after hospital discharge and maintain high levels of SARS-CoV-2-specific IgG throughout the study, which is an indicative sign of immunological memory. Thus, this work can provide useful information to better understand the diverse outcomes of severe COVID-19 pathogenesis.

IL-21 enhances STAT3/Blimp-1 signaling pathway in B cells and contributes to plasma cell differentiation in newly diagnosed patients with myasthenia gravis

The transcription factor Blimp-1 is necessary for the B cell differentiation toward immunoglobulin-secreting plasma cells. However, the immunopathological mechanisms of Blimp-1 that regulates B cell differentiation remain unclear in MG. The purpose of this study was to perform a quantitative and functional analysis of Blimp-1 in MG. A total of 34 patients with MG (18 ocular MG (OMG) and 16 generalized MG (GMG) and 20 healthy controls (HC) were recruited in this study. CD19⁺ B cells were isolated by positive selection using CD19 beads. The expression of Blimp-1 and p-STAT3 protein in isolated B cells was assessed by Western blot. Plasma cells were analyzed by flow cytometry. Serum IL-21 levels were detected by ELISA. Our data demonstrated that Blimp-1 in peripheral blood B cell of MG patients was significantly increased compared with HC. The increased expression of Blimp-1 was positively associated with clinical severity score (QMGs), plasma cell frequency, and serum IL-21 levels. Furthermore, glucocorticoid (GC) treatment reduced the expression of Blimp-1 and p-STAT3 in B cells, and this change was accompanied with relieved clinical severity, reduced plasma cell frequency, and decreased serum IL-21 levels. In vitro assay demonstrated that IL-21 stimulation upregulated STAT3 phosphorylation, increased Blimp-1 expression in B cells, and promoted plasma cell differentiation, and these processes could be inhibited by dexamethasone or STAT3 inhibitor stattic. This work indicates for the first time that aberrant expression of Blimp-1 exists on B cells and contributes to the plasma cell differentiation in MG patients. Modulation of IL-21/STAT3/Blimp-1 signaling pathway in B cells may be one of the mechanisms of glucocorticoid in the treatment of MG.

Kidney Failure Associates With T Cell Exhaustion and Imbalanced Follicular Helper T Cells

Individuals with kidney failure are at increased risk of cardiovascular events, as well as infections and malignancies, but the associated immunological abnormalities are unclear. We hypothesized that the uremic milieu triggers a chronic inflammatory state that, while accelerating atherosclerosis, promotes T cell exhaustion, impairing effective clearance of pathogens and tumor cells. Clinical and demographic data were collected from 78 patients with chronic kidney disease (CKD) (n = 42) or end-stage kidney disease (ESKD) (n = 36) and from 18 healthy controls (HC). Serum cytokines were analyzed by Luminex. Immunophenotype of T cells was performed by flow cytometry on peripheral blood mononuclear cells. ESKD patients had significantly higher serum levels of IFN-γ, TNF-α, sCD40L, GM-CSF, IL-4, IL-8, MCP-1, and MIP-1β than CKD and HC. After mitogen stimulation, both CD4+ and CD8+ T cells in ESKD group demonstrated a pro-inflammatory phenotype with increased IFN-γ and TNF-α, whereas both CKD and ESKD patients had higher IL-2 levels. CKD and ESKD were associated with increased frequency of exhausted CD4+ T cells (CD4+KLRG1+PD1+CD57-) and CD8+ T cells (CD8+KLRG1+PD1+CD57-), as well as anergic CD4+ T cells (CD4+KLRG1-PD1+CD57-) and CD8+ T cells (CD8+KLRG1-PD1+CD57-). Although total percentage of follicular helper T cell (TFH) was similar amongst groups, ESKD had reduced frequency of TFH1 (CCR6-CXCR3+CXCR5+PD1+CD4+CD8-), but increased TFH2 (CCR6-CXCR3-CXCR5+PD1+CD4+CD8-), and plasmablasts (CD3-CD56-CD19+CD27highCD38highCD138-). In conclusion, kidney failure is associated with pro-inflammatory markers, exhausted T cell phenotype, and upregulated TFH2, especially in ESKD. These immunological changes may account, at least in part, for the increased cardiovascular risk in these patients and their susceptibility to infections and malignancies.

Kinetics of humoral deficiency in CART19-treated children and young adults with acute lymphoblastic leukaemia

CD19-CAR T-cell therapy (CART19) causes B-cell aplasia (BCA) and dysgammaglobulinemia but there is a lack of information about the degree of its secondary immunodeficiency. We conducted a prospective study in children and young adults with acute lymphoblastic leukaemia treated with CART19, analysing the kinetics of BCA and dysgammaglobulinemia during therapy, as well as the B-cell reconstitution in those with CART19 loss. Thirty-four patients were included (14 female) with a median age at CART19 infusion of 8.7 years (2.9–24.9). Median follow-up after infusion was 7.1 months (0.5–42). BCA was observed 7 days after infusion (3–8), with persistence at 24 months in 60% of patients. All patients developed a progressive decrease in IgM and IgA: 71% had undetectable IgM levels at 71 days (41–99) and 13% undetectable IgA levels at 185 days (11–308). Three of 12 patients had protective levels of IgA in saliva. In two of three patients who lost CART19, persistent B-cell dysfunction was observed. No severe infections occurred. In conclusion, BCA occurs soon after CART19 infusion, with a progressive decrease in IgM and IgA, and with less impairment of IgA, suggesting the possibility of an immune reservoir. A persistent B-cell dysfunction might persist after CART19 loss in this population.

Composition of the murine gut microbiome impacts humoral immunity induced by rabies vaccines

BACKGROUND

Gut microbiome plays a crucial role in modulating human and animal immune responses. Rabies is a fatal zoonosis causing encephalitis in mammals and vaccination is the most effective method to control and eliminate rabies. The relationship between the gut microbiome and humoral immunity post rabies vaccination has not been investigated yet.

METHODS

Mice orally administrated with a cocktail of broad-spectrum antibiotics were inoculated with rabies vaccines, and humoral immune response was analyzed at indicated time points. The 16S ribosomal RNA (16S rRNA) gene sequencing was performed on fecal samples from groups in vancomycin-treated and untreated mice. Mice were immunized with rabies vaccines and virus-neutralizing antibody (VNA) levels were measured, resulting in VNA high (H) and low (L) groups. Then 16S rRNA gene sequencing was performed on fecal samples from H and L group mice.

RESULTS

After antibiotic (Abx) treatment, mice had decreased levels of rabies virus (RABV)-specific IgM, IgG, and virus-neutralizing antibody compared with untreated mice. Abx-treated mice had fewer T follicular helper cells, germinal center B cells, and antibody secreting cells (ASCs) in lymph nodes than did untreated mice. Gut microbiome facilitated secondary immune responses by increasing the generation of ASCs. Treatment with vancomycin alone had a similarly impaired effect on the humoral immune responses compared with Abx-treated mice. From the natural population group of mice received rabies vaccines, VNA titers vary significantly and the abundance of Clostridiales and Lachnospiraceae was positively associated with the antibody titers in mice.

CONCLUSIONS

Our results provide the evidence that the gut microbiome impacts humoral immunity post rabies vaccination, and further investigation of the mechanism will help the development of novel adjuvants and vaccines.

Post-rituximab immunoglobulin M (IgM) hypogammaglobulinemia

Rituximab is a B cell depleting monoclonal antibody that targets the B cell-specific cell surface antigen CD20 and is currently used to treat several autoimmune diseases. The elimination of mature CD20-positive B lymphocytes committed to differentiate into autoantibody-producing plasma cells is considered to be the major effect of rituximab, that makes it a beneficial biological agent in treating autoimmune diseases. Hypogammaglobulinemia has been reported after rituximab therapy in patients with lymphoma and rheumatoid arthritis. Similar data are scarce for other autoimmune diseases. Low immunoglobulin G (IgG) or hypogammaglobulinemia has attracted the most attention because of its significant role in protective immunity. However, the incidence and clinical implications of low immunoglobulin M (IgM) or hypogammaglobulinemia have not been studied in detail. This review will focus on the frequency and the clinical concerns of low IgM levels that result as a consequence of the administration of rituximab. The etiopathogenic mechanisms underlying post-rituximab IgM hypogammaglobulinemia and its implications are presented. The long-term consequences, if any, are not known or documented. Multiple factors may be involved in whether IgG or IgM decreases secondary to rituximab therapy. It is possible that the autoimmune disease itself may be one of the important factors. The dose, frequency and number of infusions appear to be important variables. Post-rituximab therapy immunoglobulin levels return to normal. During this process. IgM levels take a longer time to return to normal levels when compared to IgG or other immunoglobulins. IgM deficiency persists after B cell repopulation to normal levels has occurred. Laboratory animals and humans deficient in IgM can have multiple infections. Specific pharmacologic agents or biologic therapy that address and resolve IgM deficiency are currently unavailable. If the clinical situation so warrants, then prophylactic antibiotics may be indicated and perhaps helpful. Research in this iatrogenic phenomenon will provide a better understanding of not only the biology of IgM, but also the factor(s) that control its production and regulation, besides its influence if any, on rituximab therapy.

Function and dysfunction of plasma cells in intestine

As the main player in humoral immunity, antibodies play indispensable roles in the body's immune system. Plasma cells (PCs), as antibody factories, are important contributors to humoral immunity. PCs, recognized by their unique marker CD138, are always discovered in the medullary cords of spleen and lymph nodes and in bone marrow and mucosal lymphoid tissue. This article will review the origin and differentiation of PCs, characteristics of short- and long-lived PCs, and the secretion of antibodies, such as IgA, IgM, and IgG. PCs play a crucial role in the maintenance of intestinal homeostasis using immunomodulation though complex mechanisms. Clearly, PCs play functional roles in maintaining intestinal health, but more details are needed to fully understand all the other effects of intestinal PCs.

Immune regulation by glucocorticoids can be linked to cell type-dependent transcriptional responses

A functional genomics approach uncovers previously undescribed cell type–dependent responses that can be linked to the immunoregulatory actions of glucocorticoids in humans.

Glucocorticoids remain the most widely used immunosuppressive and anti-inflammatory drugs, yet substantial gaps exist in our understanding of glucocorticoid-mediated immunoregulation. To address this, we generated a pathway-level map of the transcriptional effects of glucocorticoids on nine primary human cell types. This analysis revealed that the response to glucocorticoids is highly cell type dependent, in terms of the individual genes and pathways affected, as well as the magnitude and direction of transcriptional regulation. Based on these data and given their importance in autoimmunity, we conducted functional studies with B cells. We found that glucocorticoids impair upstream B cell receptor and Toll-like receptor 7 signaling, reduce transcriptional output from the three immunoglobulin loci, and promote significant up-regulation of the genes encoding the immunomodulatory cytokine IL-10 and the terminal-differentiation factor BLIMP-1. These findings provide new mechanistic understanding of glucocorticoid action and emphasize the multifactorial, cell-specific effects of these drugs, with potential implications for designing more selective immunoregulatory therapies.

Cell-penetrating Peptides: Efficient Vectors for Vaccine Delivery

Subunit vaccines are composed of pathogen fragments that, on their own, are generally poorly immunogenic. Therefore, the incorporation of an immunostimulating agent, e.g. adjuvant, into vaccine formulation is required. However, there are only a limited number of licenced adjuvants and their immunostimulating ability is often limited, while their toxicity can be substantial. To overcome these problems, a variety of vaccine delivery systems have been proposed. Most of them are designed to improve the stability of antigen in vivo and its delivery into immune cells. Cell-penetrating peptides (CPPs) are especially attractive component of antigen delivery systems as they have been widely used to enhance drug transport into the cells. Fusing or co-delivery of antigen with CPPs can enhance antigen uptake, processing and presentation by antigen presenting cells (APCs), which are the fundamental steps in initiating an immune response. This review describes the different mechanisms of CPP intercellular uptake and various CPP-based vaccine delivery strategies.

Blimp-1-Mediated Pathway Promotes Type I IFN Production in Plasmacytoid Dendritic Cells by Targeting to Interleukin-1 Receptor-Associated Kinase M

Plasmacytoid dendritic cells (pDCs) are a specialized subset of DCs capable of rapidly producing copious amounts of type I IFN (IFN-I) in response to viral infections. The mechanism regulating rapid production of IFN-I after pDCs are exposed to viral nucleic acids remains elusive. Here, we show that the transcription factor Blimp-1 is promptly induced in pDCs after exposure to TLR7 and TLR9 ligands via a unique Ras-related C3 botulinum toxin substrate (Rac)-mediated pathway. Deletion of the Prdm1 gene encoding Blimp-1 impaired production of IFN-I, but not other cytokines, upon viral infection or treatment with CpG DNA in pDCs. Accordingly, mice lacking Blimp-1 in DCs failed to produce IFN-I after CpG stimulation and did not mount proper antiviral responses following flavivirus infection. The development of pDCs in bone marrow as well as the induction of several activation markers, such as CD86, CD69, and MHCII, by CpG stimulation was generally not affected by the absence of Blimp-1. Mechanistically, we found that Blimp-1 controls the activation of IKKα and IRF7 by directly suppressing interleukin-1 receptor-associated kinase 3 (Irak3), a negative regulator of TLR signaling, in pDCs. Together, we identify a Blimp-1-dependent pathway that rapidly facilitates IFN-I production by relieving interleukin-1 receptor-associated kinase M, encoded by Irak3, in pDCs.

Production and characterization of Newcastle disease antibody as a reagent to develop a rapid immunodiagnostic test tool

AIM

This research was conducted to produce and characterize ND antibody as reagent candidate to develop a rapid immunodiagnostic test tool.

MATERIALS AND METHODS

Four New Zealand White rabbits were used in this study and divided into two groups. First group was injected by Sato ND antigen, and second group was injected by genotype VII ND antigen. This study is divided into three steps: (a) ND antibody production, (b) ND antibody purification, and (c) ND antibody characterization. First group was rabbit injected by Sato NDV (5×108.25 egg lethal doses (ELD)50/ml) and second group was injected by genotype VII NDV (5×106.5 ELD50/ml). Antigen induction was performed by subcutaneous administrated for first (day 1) and second (day 14) injection and intravenous administrated for third (day 30) injection. Blood was collected on day 8 after third injection.

RESULTS

Antibody production increased on second antigen injection and reached a peak on day 9 after second antigen injection. Sato and genotype VII ND antibody can be produced without adjuvant within 38 days with the highest titer 210. Based on antibody titer data, both antigens induced antibody production in a similar trend. The characterization antibody by SDS-PAGE indicated that molecular weight of immunoglobulin G (IgG) is 154.93 kDa (whole IgG), heavy chain 54.39 kDa, and light chain 27.74 kDa. ND antibodies have specificity to homologous and heterologous NDVs in varying virulence.

CONCLUSION

Sato and genotype VII ND antibodies have been successfully produced within 38 days without adjuvant. Specificity of ND antibodies to NDVs in varying virulence and cross-reaction between Sato ND antibody and genotype VII ND antibody indicates that the characterized ND antibodies can be used as a reagent to develop rapid immunodiagnostic test tools.

Immunoglobulin gene analysis as a tool for investigating human immune responses

The human immunoglobulin repertoire is a hugely diverse set of sequences that are formed by processes of gene rearrangement, heavy and light chain gene assortment, class switching and somatic hypermutation. Early B cell development produces diverse IgM and IgD B cell receptors on the B cell surface, resulting in a repertoire that can bind many foreign antigens but which has had self-reactive B cells removed. Later antigen-dependent development processes adjust the antigen affinity of the receptor by somatic hypermutation. The effector mechanism of the antibody is also adjusted, by switching the class of the antibody from IgM to one of seven other classes depending on the required function. There are many instances in human biology where positive and negative selection forces can act to shape the immunoglobulin repertoire and therefore repertoire analysis can provide useful information on infection control, vaccination efficacy, autoimmune diseases, and cancer. It can also be used to identify antigen-specific sequences that may be of use in therapeutics. The juxtaposition of lymphocyte development and numerical evaluation of immune repertoires has resulted in the growth of a new sub-speciality in immunology where immunologists and computer scientists/physicists collaborate to assess immune repertoires and develop models of immune action.

EBV epigenetically suppresses the B cell-to-plasma cell differentiation pathway while establishing long-term latency

Mature human B cells infected by Epstein-Barr virus (EBV) become activated, grow, and proliferate. If the cells are infected ex vivo, they are transformed into continuously proliferating lymphoblastoid cell lines (LCLs) that carry EBV DNA as extra-chromosomal episomes, express 9 latency-associated EBV proteins, and phenotypically resemble antigen-activated B-blasts. In vivo similar B-blasts can differentiate to become memory B cells (MBC), in which EBV persistence is established. Three related latency-associated viral proteins EBNA3A, EBNA3B, and EBNA3C are transcription factors that regulate a multitude of cellular genes. EBNA3B is not necessary to establish LCLs, but EBNA3A and EBNA3C are required to sustain proliferation, in part, by repressing the expression of tumour suppressor genes. Here we show, using EBV-recombinants in which both EBNA3A and EBNA3C can be conditionally inactivated or using virus completely lacking the EBNA3 gene locus, that-after a phase of rapid proliferation-infected primary B cells express elevated levels of factors associated with plasma cell (PC) differentiation. These include the cyclin-dependent kinase inhibitor (CDKI) p18INK4c, the master transcriptional regulator of PC differentiation B lymphocyte-induced maturation protein-1 (BLIMP-1), and the cell surface antigens CD38 and CD138/Syndecan-1. Chromatin immunoprecipitation sequencing (ChIP-seq) and chromatin immunoprecipitation quantitative PCR (ChIP-qPCR) indicate that in LCLs inhibition of CDKN2C (p18INK4c) and PRDM1 (BLIMP-1) transcription results from direct binding of EBNA3A and EBNA3C to regulatory elements at these loci, producing stable reprogramming. Consistent with the binding of EBNA3A and/or EBNA3C leading to irreversible epigenetic changes, cells become committed to a B-blast fate <12 days post-infection and are unable to de-repress p18INK4c or BLIMP-1-in either newly infected cells or conditional LCLs-by inactivating EBNA3A and EBNA3C. In vitro, about 20 days after infection with EBV lacking functional EBNA3A and EBNA3C, cells develop a PC-like phenotype. Together, these data suggest that EBNA3A and EBNA3C have evolved to prevent differentiation to PCs after infection by EBV, thus favouring long-term latency in MBC and asymptomatic persistence.

Influence of maternal vaccination against diphtheria, tetanus, and pertussis on the avidity of infant antibody responses to a pertussis containing vaccine in Belgium

Maternal antibodies induced by vaccination during pregnancy cross the placental barrier and can close the susceptibility gap to pertussis in young infants up to the start of primary immunization. As not only the quantity but also the quality of circulating antibodies is important for protection, we assessed whether maternal immunization affects the avidity of infant vaccine-induced IgG antibodies, in the frame of a prospective clinical trial on pregnancy vaccination in Belgium. Infants born from Tdap (Boostrix®) vaccinated (N = 55) and unvaccinated (N = 26) mothers were immunized with a hexavalent pertussis containing vaccine (Infanrix Hexa®) at 8, 12 and 16 weeks, followed by a fourth dose at 15 months of age. Right before and one month after this fourth vaccine dose, the avidity of IgG antibodies against diphtheria toxin (DT), tetanus toxin (TT), pertussis toxin (PT), filamentous hemagglutinin (FHA) and pertactin (Prn) was determined using 1.5 M ammonium thiocyanate as dissociating agent. In both groups, antibody avidity was moderate for TT, PT, FHA and Prn and low for DT after priming. After a fourth dose, antibody avidity increased significantly to high avidity for TT and PT, whereas it remained moderate for FHA and Prn and low for DT. The avidity correlated positively with antibody level in both study groups, yet not significantly for PT. When comparing both study groups, only PT-specific antibodies showed significantly lower avidity in infants born from vaccinated than from unvaccinated mothers after the fourth vaccine dose. The clinical significance of lower avidity of vaccine induced infant antibodies after maternal vaccination, if any, needs further investigation.