Here, we described a patient where infections and autoimmune phenomena resulted to be embedded in a very complex clinical picture. Since her first years of life, the child showed a striking predisposition to develop infectious illnesses, which were mostly located in the respiratory system. They never reached aspects of great severity, such as meningitis/encephalitis or sepsis, but the frequent involvement of lungs (including CMV pneumonia), the occurrence of oral candidiasis after the first year of life, the recurrent/chronic diarrhea and, finally, the development of chronic sinusitis with extensive nasal polyps resulted to be quite concerning, of course. However, despite all the above clinical issues, no classified primary ID could have been demonstrated, through several and repeated immunologic investigations. According to clinical criteria (e.g. warning signs or red flags, edited by Jeffrey Modell Foundation), a condition of immunodeficiency was very likely and other diseases, resembling ID clinically (such as mucoviscidosis and primary ciliary diskinesia), have been ruled out as well.
A secondary ID was considered in the differential diagnosis, because of the onset of autoimmune manifestations consistent with a diagnosis of SLE. Patients affected with SLE can develop symptoms of immunodeficiency, which is often due to drug therapy. However, several functional defects have been described apart from the ongoing treatment, namely reduced phagocytic activity, lymphopenia/neutropenia, altered T-cell activation and reduction of NK cells, by instance [14
]. Therefore, SLE is associated to a greater occurrence of infections, which represent a major cause of morbidity and mortality and can promote the occurrence of a complication known as macrophage activation syndrome (MAS), which was manifested by our patient too [16
]. Actually, the diagnosis of SLE was made at 7-8 years of age, which is much later than the onset of the infectious burden, being recorded since the first year of life. Thus, SLE and related therapy (including steroids) could not justify the whole clinical history, in light of current knowledge.
Another interesting aspect was the precocious CMV infection: it rarely causes symptomatic and severe disease, such as pneumonia, in the immune-competent host.18 Congenital CMV infection was ruled out and, thus, the patient was supposed to have developed a post-natal infection. Precocious CMV infection can associate to cellular immunodeficiency [18
], but the patient did not show a severe combined immunodeficiency (SCID) and no significant abnormalities have been found trough the analysis of lymphocyte phenotype and in vitro proliferation. Conversely, it is known that herpes viruses, including CMV, interact with immune system in a complex manner: several immune cells (including monocytes, macrophages and dendritic cells) represent an important viral target and site of latency; moreover, CMV genome has been showed to encode also several products, including analogues of cytokines, which can interfere with the immune responses. Although CMV is known to induce unbalances of T cells (especially in term of CD4/CD8 ratio) and hypo-responsiveness to mitogens and antigens in lymphocyte during the early phases of the infection, actually no long-term immune-dysregulation could be demonstrated. However, some evidences are emerging, that CMV might alter the homeostasis of the immune system somehow, but that does not seem to be enough in order to provide a sufficient explanation of the complexity of the clinical history we reported, based on the current knowledge [19
]. Thus, the hypothesis of a secondary ID (because of infections or rheumatic diseases or drugs) is not sufficiently supported in this clinical case.
Several primary IDs have been consistently associated to the development of SLE, such as some complete defects of one of precocious components of the classic pathway of complement system, complete IgA deficiency and chronic granulomatous disease. By instance, C1q, C4, C1r-s and C2 deficits have an occurrence of SLE equal to 93%, 75%, 57% and 25%, respectively. An altered clearance of immune complexes has been supposed as a main pathologic mechanism, although a direct role of complement system in the lymphocyte immune tolerance (through the elimination of auto-reactive lymphocytes) emerged from experimental animal models [21
]. Moreover, many other primary IDs are less frequently reported to develop SLE, including several antibody defects (IgG subclass deficiency, hyper-IgE syndrome, hyper-IgM syndrome and CVID) [12
A complement deficiency was excluded, through a complete analysis of all components of complement system. Moreover, antibody deficiency was excluded many times during infancy and childhood, until she developed a significant (IgA + IgG) hypo-gammaglobulinemia, when she was around 9 years. Which was later than onset of both the infectious issue and autoimmune phenomena? Only at this time, the immunological features fulfilled the criteria for a diagnosis of CVID.
In addition to the respiratory and gastro-intestinal recurrent infections (and also an increased risk of malignancy), CVID is characterized by a significant prevalence of autoimmune manifestations: 25-30% cases usually develop autoimmunity during the course of the disease and many are immune-mediated cytopenias (anemia and thrombocytopenia) [23
Several functional and phenotypic abnormalities of lymphocytes have been described in the setting of CVID, which are not limited to B cells, but involve T cells, monocyte-macrophages and antigen-presenting cells too. All these observations supported a vision that CVID is a heterogeneous group of diseases, deriving from different pathogenetic defects leading an impaired production of antibodies, in addition to other and variable clinical manifestations. This statement is supported by the genetic of CVID, which resulted to be very variable and linked to a complex (and largely unknown) multi-factorial causal pattern. Indeed, several molecular mutations (at least five) have been found in the small part (around 10% cases) of CVID where a genetic aberration could have been demonstrated [24
Among multiple immune abnormalities recorded in CVID, special attention should be paid to the development of memory B cells. A study published in 2002 by Warnatz et al., who had initially observed a memory deficit in patients affected with X-linked hyper-IgM syndrome [27
]. This and other works led to so-called “Freiburg classification” of CVID patients, based on the phenotype of CD27+ memory B cells, which are divided in two main types: i) IgD+CD27+ “unswitched” memory B cells, producing IgM almost exclusively; ii) IgD-CD27+ “switched” memory B cells, being able to produce IgG and IgA, in addition to IgM [28
]. Recently, thanks to a multi-centric study (EURO-Trial), considering more than 300 CVID patients, this classification was refined. First, CVID patients were divided according to the number of peripheral B cells: <1% (B- patients) or >1% (B+ patients). The latter group of patients showed a deficit in the memory compartment, being more or less severe. SmB+ patients conserved >2% of switched memory B cells out of the total CD19+ B cells, whereas SmB- patients have a number of switched memory B cells <2% [29
The child showed a reduced B cell count (4% of peripheral lymphocytes) and, of these, a percentage <2% was constituted by switched memory B cells. Therefore, according to EURO-trial classification, the patient was in B+SmB-. Interestingly, this group was characterized by a greater prevalence of non-infectious complications, such as diffuse adenopathy, splenomegaly, granulomatous lesions and autoimmunity [29
Therefore, CVID patients have been classified into subgroups according to their B cell count and their memory B cell profile and, finally, based on further B cell sub-population, such as activated B cells (IgD+IgM+CD27-CD21low
) or transitional B cells (IgD+IgM+CD27-CD21+/low
In reference to the phenotype analysis of lymphocytes performed after CVID diagnosis, the patient showed a percentage of CD21low
B cells greater than 30%. An expansion of CD21low
B cell population (>10% of circulating B cells) has been associated to the presence of spleen enlargement and autoimmune phenomena [29
However, in our patient, it is outstanding that the abnormalities of B memory and, particularly, the deficit of switched memory B cells, had been noticed before the development of hypo-gammaglobulinemia. This finding prompted two observations.
First, it might be speculated that antibody deficiency could have been the final step of a “deteriorating” process of the immune system and that some immune abnormalities, namely B memory deficit (used to classify CVID), could come up earlier. Thus, it might be useful to look for these immune aberrations in those clinical settings, characterized by increased susceptibility to infections and autoimmune phenomena, which cannot be diagnosed as a specific rheumatic disease or a well-defined primary ID.
Second, patients suffering with CVID might have a personal history of recurrent infections even before the development of a quantitative antibody deficiency, which is the hallmark of CVID, according to current diagnostic criteria. Here, it seems that a deficit of memory B-cell function, which is a fundamental component of the humoral defense, might arise before the hypo-gammaglobulinemia. Such an observation might provide a valuable explanation why the patient developed a clinical phenotype of recurrent/chronic respiratory infections and enterophaty, even though no quantitative humoral deficiency had been evidenced yet. It might be that the production of antibody was not qualitatively effective (because of the memory impairment); or that the B cell unbalance could reflect an impairment of other immune components, maybe a deficit in T cells helping the full development of B cell response.
In fact, the pathogenetic defects in CVID, which is considered an antibody-related primary ID, could actually be inside the T lymphocyte rather than inside B cell. By instance, among few known CVID-related genetic defects, one involved ICOS molecule, which is expressed on T lymphocyte [34
]. Thus, CVID could theoretically derive from a primary defect in any component of the immune system (T lymphocytes and APCs) supporting B cell proliferation, isotype switching and memory development. Such a vision might explain those cases where recurrent infections, severe complications such as MAS and the development of autoimmunity and lymphoproliferative phenomena have occurred before or independently from the presence of quantitative antibody deficiency.
In conclusion, unusual and recurrent infections may precede the occurrence of a quantitative deficit of antibody in CVID as well as some autoimmune phenomena do, which are known to be associated to some primary immune-deficiencies [35
]. Moreover, we speculate that the B memory defect, considered useful in the classification of CVID patients (once such a diagnosis has been made) may be evidenced before the development of serum immunoglobulin deficiency. In this clinical setting, a B memory defect might alert for a potential evolution to CVID in those patients where infections and autoimmunity cannot be clearly diagnosed as specific rheumatic disease or primary immunodeficiency, in light of current diagnostic criteria.