Complement C2 deficiency disarranging innate and adaptive humoral immune responses in a pediatric patient: Treatment with rituximab


  • Fabian Hauck,

    Corresponding author
    1. University Medical Center Carl-Gustav-Carus, Technical University, Dresden, Germany, and Helmholtz Centre for Infection Research, Braunschweig, Germany
    Current affiliation:
    1. INSERM, Paris, France
    • INSERM, Unité U768, Laboratoire du Développement Normal et Pathologique du Système Immunitaire, Paris, France
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  • Min Ae Lee-kirsch,

    1. University Medical Center Carl-Gustav-Carus, Technical University, Dresden, Germany
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  • Daniela Aust,

    1. University Medical Center Carl-Gustav-Carus, Technical University, Dresden, Germany
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  • Joachim Roesler,

    1. University Medical Center Carl-Gustav-Carus, Technical University, Dresden, Germany
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    • Drs. Roesler and Pessler contributed equally to this work.

  • Frank Pessler

    1. Helmholtz Centre for Infection Research, Braunschweig, Germany
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    • Drs. Roesler and Pessler contributed equally to this work.


Complement deficiencies (CDs) are classified as primary immunodeficiency disorders (PIDs) because diminished opsonization or the inability to form the membrane attack complex increases the susceptibility to pyogenic bacterial infections (1). Moreover, diverse autoimmune manifestations occur that vary with the particular CD (1–3). Complement C2 deficiency (C2D; MIM217000) is classically associated with early-onset invasive pneumococcal infections and systemic lupus erythematosus (SLE) or SLE-like manifestations, which typically present in early or middle adulthood (3, 4). Due to its low prevalence (∼1:20,000) (4) and variable clinical manifestations, publications on the treatment of C2D are scarce.

In this case report, we describe a C2D patient with the earliest onset of SLE published, to our best knowledge, thus far. We report on rare complications such as immune complex–mediated leukocytoclastic vasculitis (LCV), destructive follicular bronchiolitis (DFB) with polyclonal B cell proliferation, and disturbed humoral immune responses, including dysgammaglobulinemia and specific antibody deficiency, therefore defining a novel phenotype. Providing a detailed histologic, immunologic, and genetic workup, we discuss the pathophysiology of C2D as a complex disorder at the interface between innate and adaptive humoral immunity. Finally, we describe, for the first time, the effective treatment with rituximab (RTX), implicating B cell depletion as a therapeutic strategy for the autoimmune manifestations of the PID.

Case report

The 4-year-old daughter of nonconsanguineous parents presented with chronic relapsing purpura predominantly of the lower extremities, oligoarthritis of the knee and talocalcaneal joints, and abdominal pain. She was erroneously diagnosed with Henoch-Schönlein purpura and treated by her primary pediatrician with ibuprofen. At the age of 6 years she experienced another episode of purpura (Figure 1A) and oligoarthritis after jumping into cold water and was admitted to our hospital. Her medical history included chronic pruritic efflorescence (Figure 1B) between phases of acute purpura, photosensitivity with malar rash, diffuse hair loss, headache, abdominal pain, low body weight, and fatigue.

Figure 1.

A, Acute palpable purpura of the lower extremities and lower trunk provoked by cold water exposure. B, Chronic macular and papular efflorescences of the lower extremities with single central urticarial lesions and signs of scratching due to pruritus. C, Hematoxylin and eosin stain of a lesional skin biopsy sample, demonstrating corium with perivascular and interstitial neutrophilic and eosinophilic infiltrate with neutrophilic nuclear fragments, swollen endothelium, and fibrinoid vessel degeneration with moderate erythrocytic extravasation being compatible with leukocytoclastic vasculitis. D, Immunohistochemical stain showing perivascular deposition of IgM in the duodenal mucosa (C3 and IgA were detectable as well but are not shown).

Clinical and ultrasound examinations of the knee and talocalcaneal joints revealed acute synovitis with joint effusion. However, the radiographs did not show bone erosions or osteopenia. The results of a lesional skin biopsy were consistent with cutaneous LCV (Figure 1C). Abdominal sonography displayed mesenteric lymphadenopathy and segmental inflammation of the transverse colon. Immunohistochemical analysis of the biopsy samples taken during gastroduodenoscopy showed perivascular deposition of C3, IgM, and IgA in gastric and duodenal mucosa (Figure 1D). Body temperature, C-reactive protein (CRP) level, complete blood count, lymphocyte subpopulations, coagulation parameters, and platelet function were normal. The erythrocyte sedimentation rate was higher at 4°C (52 mm/hour) than at room temperature (20 mm/hour), but cryoglobulins or cryofibrinogens were not detected. A comprehensive evaluation for viral, bacterial, fungal, or parasitic infections gave negative results. Serum IgM was increased, while IgG2 and IgG4 were decreased (Table 1). Antimicrobial IgM antibody serum levels were elevated nonspecifically. IgM allohemagglutinins and specific antibodies against protein antigens were present and increased after a booster vaccination. Serum was negative for antinuclear antibodies (ANAs), extractable nuclear antigens, double-stranded DNA (dsDNA), antineutrophil cytoplasmic antibodies, rheumatoid factor, or C1q-binding immune complexes, but was positive for anti-C1q, anticardiolipin IgM, and C3d-binding immune complexes (Table 1). Strikingly, classical complement pathway activity (CH50) was absent, while the alternative pathway activity (AH50) and the mannose-binding lectin concentration were normal. C1q and C3 levels were normal, and the C4 level was reduced insignificantly. In contrast, C2 activity was undetectable (Table 1). The patient was homozygous for HLA–A*25, HLA–B*18, and HLA–DRB1*15, a haplotype linked to C2D type 1, which is characterized by defective C2 synthesis. Sequencing of complementary DNA and genomic DNA revealed the previously described homozygous 28-bp deletion (c.841-849+19del28) in the C2 gene (NM_000063), therefore confirming the diagnosis of complete C2D (5).

Table 1. Immunologic parameters of the C2 deficiency systemic lupus erythematosus patient*
 PatientAge-matched norm
  • *

    Immunoglobulin concentrations were determined by nephelometry. nd = not defined; HBs-Ag = hepatitis B surface antigen; aCL = anticardiolipin antibody; CIC = circulating immune complex; GPt = gigaparticle.

CH50, %<165–135
AH50, %8660–140
Mannose-binding lectin, ng/ml2,927>50
C1q, mg/dl11.65–25
C4, mg/dl0.150.17–0.38
C2, %<265–135
C3, gm/liter2.01<1.67
C3d, μU/liter10.0<40
Allohemagglutinins (blood group B)  
IgM, gm/liter2.750.40–1.60
IgG, gm/liter10.66.0–13.0
IgG1, gm/liter6.673.5–9.1
IgG2, gm/liter0.330.85–3.30
IgG3, gm/liter0.80.2–1.0
IgG4, gm/liter0.0280.03–1.58
IgA, gm/liter1.410.6–2.2
IgE, kU/liter46<330
Protein-specific antibody (HBsAg)  
 Prebooster, IU/liter41>100 protective
 Postbooster, IU/liter910Increase expected
Polysaccharide-specific antibody (pneumococcal), mg/liter  
 1 week postsepsis27.9Increase expected
 6 weeks postbooster8.9Increase expected
Anti-C1q, units/ml78.27<20
aCL-IgM, units/ml18.05<10
C3d-CIC, μg/ml47.40<40
CD19+ B cells (before rituximab), GPt/liter0.40.2–1.6
IgD+CD27− naive B cells, % of CD20+19.467.8–89.0
IgD+CD27+ marginal zone B cells, % of CD20+62.25.0–16.2
IgD−CD27+ switched memory B cells, % of CD20+16.44.0–14.0
CD21lowCD38low B cells, % of CD20+38.91.1–6.9

Before C2D was diagnosed, prednisone (2 mg/kg/day by mouth for 7 days, then tapered over 7 days) had been started to treat the purpura and the painful oligoarthritis. Four days into the treatment, the patient presented in poor clinical condition with a high fever (39.9°C) and a CRP level of 220 mg/dl (normal level <5). Streptococcus pneumonia was isolated from a blood culture. After 7 days of intravenous treatment with cefotaxime, penicillin prophylaxis was started. Serum pneumococcal antibody titers did not rise after this invasive infection or after a subsequent vaccination with a 23-valent pneumococcal polysaccharide vaccine (Table 1). At the age of 8 years, a severe combined ventilation disorder developed, possibly triggered by an upper airway infection. The CRP level was modestly elevated and peaked at 35.3 mg/dl, while IgM peaked at 3.00 mg/dl (normal range 0.40–1.60). A radiograph and a computed tomography scan of the chest showed bronchiectasis and diffuse nodular pulmonary infiltrates (Figures 2A and B). Histopathologic analysis of open lung biopsy specimens revealed polyclonal, nonmalignant, predominantly B-lymphocytic, and destructive infiltrates mostly in and around the bronchioles, but no signs of vasculitis. Epstein-Barr virus (EBV) antigens were not detected in the lesions, and EBV polymerase chain reaction was negative. DFB was therefore diagnosed (Figures 2C and D). Simultaneously, immunophenotyping of peripheral blood B cells showed reduced numbers of naive IgD+CD27− B cells, increased numbers of IgD+CD27+ marginal zone (MZ) B cells, and switched memory IgD−CD27+ B cells, as well as markedly increased CD21lowCD38low B cells, a population that is associated with autoimmune disorders such as SLE (6) (Table 1). Initial treatment with intravenous (IV) pulse methylprednisolone (3 cycles of 3 days with 20 mg/kg/day, every 3 weeks) and prednisolone (2 mg/kg/day by mouth between the cycles) induced a remission of the pulmonary disease, indicated by a recovery of the vital lung capacity from 45% to 105% of normal for age and the disappearance of the pulmonary infiltrates. Naturally, the bronchiectasis remained. B cell depletion with RTX (375 mg/m2 IV weekly for 4 weeks) was started 2 weeks into this corticosteroid course. After the third methylprednisolone pulse, prednisolone was tapered over 10 weeks to a maintenance dosage (0.5 mg/kg by mouth every other day). Total IgM declined constantly and normalized for the first time 6 months after the first RTX course. IgG declined more slowly and had to be substituted 8 months after RTX. RTX was given once more for reappearance of CD19+ B cells in peripheral blood 10 months after the initial course.

Figure 2.

A, Chest radiograph showing bronchial wall swelling without clear pneumonic infiltrate. B, Computed tomography of the chest showing bronchial wall swelling, bronchiectases, and peribronchial and pulmonary nodular infiltrates. C, Hematoxylin and eosin stain of a subpleural lung biopsy sample showing bronchiolocentric lymphocytic nodules and partially destructive bronchiolitis and peribronchiolitis without any vasculitis or malignancy. D, Immunohistochemical CD20 stain identifying the majority of lymphocytes as B cells that partially infiltrate bronchiolar epithelium being indicative for B lymphocytic destructive follicular bronchiolitis.

At 15 months of followup, the patient's lung disease remained in remission with normal pulmonary function tests. Cutaneous vasculitis and pruritus recurred during the prednisolone taper, albeit with reduced intensity, and responded well to treatment with dapsone (5 mg/kg by mouth) and cetirizine (5 mg/12 hours by mouth). The arthritis flares have become less frequent and intense since starting RTX. So far, the patient has not shown any cardiac, renal, ocular, or central nervous system manifestations.


CDs of the classical pathway are associated with pyogenic bacterial infections due to reduced pathogen opsonization and phagocytosis (1). Consequently, bacterial sepsis and meningitis predominantly caused by Streptococcus pneumoniae are common in C2D (1, 7). Homozygosity for the IgG2 allotype G2M(n) has been reported to be a protective factor in C2D, suggesting a possible compensation for the innate humoral immunodeficiency by the adaptive humoral immunity (8). However, our C2D patient displayed a marked IgG2 and modest IgG4 subclass deficiency and experienced pneumococcal sepsis shortly after oral steroids were given. This underscores the importance of an adequate antibacterial prophylaxis when CD of the classical pathway is suspected, particularly in the context of IgG subclass deficiency and/or treatment with immunosuppressive drugs. The success of the recommended pneumococcal immunization is uncertain for reasons discussed below and should be monitored.

Complete C2D was associated with SLE in 25% of the patients (4), and a mean age of 37 years at the time of SLE diagnosis was reported (9). However, SLE-related symptoms of our patient started at age 4 years, and she fulfilled 4 of the SLE diagnostic criteria (malar rash, photosensitivity, arthritis, and antiphospholipid antibodies) at age 6 years (10). To the best of our knowledge, she is therefore the youngest C2D SLE patient reported so far.

As commonly seen in C2D SLE patients (3, 9), our patient had neither ANA nor anti-dsDNA autoantibodies, but repeatedly tested positive for anti-C1q and anticardiolipin antibodies. CDs of the classical pathway contribute to the pathogenesis of SLE by 2 mechanisms: 1) reduced solubility and clearance of immune complexes and apoptotic cells and 2) impaired tolerance induction toward autoantigens by disturbed clonal deletion or anergy of autoreactive B cells (1, 4). Antigens derived from infectious agents or autoantigens from apoptotic cells are physiologically tagged by C1q, C4, C2, and C3 and form immune complexes with IgM and IgG antibodies (1). This mediates their binding to Fc receptors and specific complement receptors such as CR1 (CD35) and CR3 (CD11b) expressed by erythrocytes and most myeloid cells, and finally leads to their clearance via the monocyte/macrophage system (11). This tagging is disturbed in deficiencies of early classical complement components. According to the waste disposal hypothesis, this results in immune complex accumulation and precipitation in the small vessels of diverse end organs (1). Subsequently, they activate vascular endothelium and mast cells, which in turn release histamine and proinflammatory cytokines. The ensuing invasion of activated eosinophils and neutrophils induces LCV, pruritus, and arthritis (12). The clinical and histopathologic features of our C2D SLE patient showing skin LCV and perivascular deposition of C3, IgM, and IgA in the stomach and duodenum agree with this pathogenetic model.

Instructive abnormalities were found in IgD+CD27+ MZ B cell numbers. These cells, a distinct splenic B cell population with a prediversified B cell receptor (BCR) repertoire, proliferate and differentiate into mainly IgM-secreting plasmacytes without generating memory upon antigenic stimulation (13). Of note is that the SLE flares in our C2D patient correlated with increased levels of IgD+CD27+ MZ B cells and IgM production. Normally, C3-tagged antigens are bound by B cells and follicular dendritic cells (FDCs) via CR1 and CR2 (CD21) and retained in the germinal centers of B cell follicles (11). Therefore, B cell maturation, somatic hypermutation, class-switch recombination, and generation of B cell memory depend on innate humoral instructions (11). Especially IgD+CD27+ MZ B cells have been implicated in delivering C3-tagged antigens to FDCs in mice, thereby contributing to adaptive humoral responses (14). Moreover, C3-tagged antigens reduce the threshold of B cell activation by coligation of the BCR with the B cell coreceptor (CD19/CD21/CD81) (11).

Additionally, tagging low-affinity B cell antigens with C3d rescues cognate B cells from caspase-dependent apoptosis (11). Strikingly, our C2D SLE patient showed virtually no antibody responses after natural infection with S pneumoniae and pneumococcal vaccination and had a marked IgG2 and a modest IgG4 subclass deficiency, possibly reflecting disturbed polysaccharide trafficking to and/or retention of polysaccharide antigens in the germinal center.

Furthermore, we found signs of misguided enhanced B cell activity. Polyclonal B cell proliferation generating B cell follicle-like structures and causing DFB in our C2D SLE patient could have been induced by B cells that had escaped clonal deletion or anergy and proliferated after BCR and BCR coreceptor coligation by low-affinity antigens. CD21lowCD38low B cells are a distinct B cell population that is mainly found in autoimmunity-prone individuals (6). These B cells express highly autoreactive germline BCRs and have down-regulated an array of activating molecules or CRs in order to reach anergy (6). Since our C2D SLE patient displayed a large CD21lowCD38low B cell population and anti-C1q and anticardiolipin IgM autoantibodies, it is tempting to speculate either that reduced classical complement activity had impaired clonal deletion or that immune complex–mediated chronic stimulation of naive B cells may have been the driving source of this distinct B cell phenotype.

Because of the likely roles of B cells in the pathogenesis of our patient's autoimmune manifestations, we treated her with RTX. We believe that this treatment enabled us to taper the prednisolone without recurrence of the pulmonary pathology as documented by sustained normalized lung function over 15 months. Vasculitis and arthritis also became less frequent and intense. Moreover, the patient's IgM normalized for the first time, and there were no infectious complications associated with the RTX treatment. Recently, RTX proved effective in one patient with lupus-like nephritis due to complement C1s deficiency (15). These encouraging results from 2 patients with different genetic lesions suggest that RTX may be a useful and safe treatment for the SLE-like manifestations of early classical complement defects.

C2D patients are at increased risk of developing chronic cardiovascular disorders due to immune complex–mediated vasculitis (9). Therefore, B cell depletion may be beneficial in reducing long-term cardiovascular morbidity and mortality. The depletion of B cells by RTX in C1s- and C2-deficient patients also adds to our understanding of its mechanism of action. Clearly, RTX can mediate destruction of B cells in the absence of classical complement activity, suggesting that antibody-dependent cellular cytotoxicity may suffice (15). Taken together, this pediatric patient with C2D-associated SLE illustrates how a primarily inborn defect in innate immunity and its secondary disarrangement of humoral immune responses create diverse immunologic and rheumatologic disease manifestations, namely nonresponsiveness to pneumococcal polysaccharide antigens, dysgammaglobulinemia with elevated IgM but IgG subclass deficiency, autoantibody production, immune complex–mediated LCV, oligoarthritis, and polyclonal B cell activation–associated parenchymal lung disease.


All authors were involved in drafting the article or revising it critically for important intellectual content, and all authors approved the final version to be submitted for publication. Dr. Hauck had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Study conception and design. Hauck, Lee-Kirsch, Aust, Pessler.

Acquisition of data. Hauck, Lee-Kirsch, Aust, Roesler.

Analysis and interpretation of data. Hauck, Lee-Kirsch, Aust, Roesler, Pessler.


The authors would like to thank Drs. Anne Durandy and Capucine Picard for critically reading this manuscript and Dr. Annette Stein for reviewing the patient's skin biopsy and selecting the image shown in Figure 1C.