Neutrophils utilize immunoglobulins (Igs) to clear antigen, but their role in Ig production is unknown. Here we identified neutrophils around the marginal zone (MZ) of the spleen, a B cell area specialized in T-independent Ig responses to circulating antigen. Neutrophils colonized peri-MZ areas after post-natal mucosal colonization by microbes and enhanced their B-helper function upon receiving reprogramming signals from splenic sinusoidal endothelial cells, including interleukin 10 (IL-10). Splenic neutrophils induced Ig class switching, somatic hypermutation and antibody production by activating MZ B cells through a mechanism involving the cytokines BAFF, APRIL and IL-21. Neutropenic patients had fewer and hypomutated MZ B cells and less preimmune Igs to T-independent antigens, which indicates that neutrophils generate an innate layer of antimicrobial Ig defense by interacting with MZ B cells.

MyD88 is a key downstream adapter for most Toll-like receptors (TLRs) and interleukin-1 receptors (IL-1Rs). MyD88 deficiency in mice leads to susceptibility to a broad range of pathogens in experimental settings of infection. We describe a distinct situation in a natural setting of human infection. Nine children with autosomal recessive MyD88 deficiency suffered from life-threatening, often recurrent pyogenic bacterial infections, including invasive pneumococcal disease. However, these patients were otherwise healthy, with normal resistance to other microbes. Their clinical status improved with age, but not due to any cellular leakiness in MyD88 deficiency. The MyD88-dependent TLRs and IL-1Rs are therefore essential for protective immunity to a small number of pyogenic bacteria, but redundant for host defense to most natural infections.

Autosomal recessive interleukin-1 receptor-associated kinase (IRAK)-4 and myeloid differentiation factor (MyD)88 deficiencies impair Toll-like receptor (TLR)- and interleukin-1 receptor-mediated immunity. We documented the clinical features and outcome of 48 patients with IRAK-4 deficiency and 12 patients with MyD88 deficiency, from 37 kindreds in 15 countries. The clinical features of IRAK-4 and MyD88 deficiency were indistinguishable. There were no severe viral, parasitic, and fungal diseases, and the range of bacterial infections was narrow. Noninvasive bacterial infections occurred in 52 patients, with a high incidence of infections of the upper respiratory tract and the skin, mostly caused by Pseudomonas aeruginosa and Staphylococcus aureus, respectively. The leading threat was invasive pneumococcal disease, documented in 41 patients (68%) and causing 72 documented invasive infections (52.2%). P. aeruginosa and Staph. aureus documented invasive infections also occurred (16.7% and 16%, respectively, in 25% and 25% of patients). Systemic signs of inflammation were usually weak or delayed. The first invasive infection occurred before the age of 2 years in 53 (88.3%) and in the neonatal period in 19 (32.7%) patients. Multiple or recurrent invasive infections were observed in most survivors (n = 36/50, 72%).

Mutua Madrileña Foundation, Fondation de l'Université de Lausanne et Centre Hospitalier Universitaire Vaudois, Instituto Carlos III, CIBERER, National Institutes of Health, Generalitat de Catalunya, Fundació CELLEX.

Initiation of combined antiretroviral therapy within the first 12 weeks of life in vertically human immunodeficiency virus type 1-infected children favors the establishment of low-level proviral reservoirs. Nevertheless, treatment discontinuation in these patients may lead to rapid and irreversible expansion of reservoir size.

Human cytomegalovirus (HCMV) has been reported to reshape the NK-cell receptor (NKR) distribution, promoting an expansion of CD94/NKG2C + NK and T cells. The role of NK cells in congenital HCMV infection is ill-defined. Here we studied the expression of NKR (i.e., NKG2C, NKG2A, LILRB1, CD161) and the frequency of the NKG2C gene deletion in children with past congenital infection, both symptomatic (n = 15) and asymptomatic (n = 11), including as controls children with postnatal infection (n = 11) and noninfected (n = 20). The expansion of NKG2C + NK cells in HCMV-infected individuals appeared particularly marked and was associated with an increased number of LILRB1 + NK cells in cases with symptomatic congenital infection. Increased numbers of NKG2C + , NKG2A + , and CD161 + T cells were also associated to HCMV infection. The NKG2C deletion frequency was comparable in children with congenital HCMV infection and controls. Remarkably, the homozygous NKG2C +/+ genotype appeared associated with increased absolute numbers of NKG2C + NK cells. Moreover, HCMV-infected NKG2C +/+ children displayed higher absolute numbers of NKG2A + and total NK cells than NKG2C +/− individuals. Our study provides novel insights on the impact of HCMV infection on the homeostasis of the NK-cell compartment in children, revealing a modulatory influence of NKG2C copy number. Eur. J. Immunol. 2012. 42: 3256-3266 Immunity to infection 3257 lifelong latent state, occasionally undergoing reactivation, but may have a pathogenic role in immunodeficient and immunosuppressed patients [1][2][3]. Moreover, HCMV has been associated with atherosclerosis, lymphoproliferative disorders, and glioblastoma, as well as with an accelerated immunosenescence and a shorter lifespan [4][5][6][7]. Vertical transmission of HCMV during pregnancy is considered the most common cause of congenital infection worldwide, affecting ∼0.2-2% of infants and potentially causing fetal lesions [8][9][10]. Though most infected newborns are asymptomatic, ∼10% display a variety of clinical disorders [8,11] potentially leading to important sequelae such as mental retardation and deafness. The type of maternal infection (i.e., primary versus reactivation/reinfection) conditions the risk of congenital infection and the pregnancy stage at which transmission occurs is related to clinical severity [12][13][14][15][16]. Maternal antibodies with neutralizing activity are transferred to the fetus predominantly during the third trimester of gestation and may prevent congenital CMV disease [17]. Among other factors, fetal immune immaturity may determine the outcome of congenital infection [18,19]. An effective defense against HCMV requires the participation of T and NK cells, and the virus has developed different immune evasion strategies [20]. Patients with congenital HCMV infection have been shown to display mature CD8 + T-cell responses [21,22], and an expansion and differentiation of a specific TcR γδ + cell subset has been recently reported [23]. In contrast, information on the role of...

Multisystem inflammatory syndrome associated with the SARS-CoV-2 pandemic has recently been described in children (MIS-C), partially overlapping with Kawasaki disease (KD). We hypothesized that: 1) MIS-C and pre-pandemic KD cytokine profiles may be unique and justify the clinical differences observed; 2) SARS-CoV-2-specific immune complexes (IC) may explain the immunopathology of MIS-C. Seventy-four children were included: 14 MIS-C; 9 patients with positive SARS-CoV-2-PCR without MIS-C (COVID); 14 pre-pandemic KD and 37 healthy controls (HC). Thirty-four circulating cytokines were quantified in pre-treatment serum or plasma samples and the presence of circulating SARS-CoV-2 IC was evaluated in MIS-C patients.Compared to HC, MIS-C and KD groups showed most cytokines to be significantly elevated, with IFN-γ-induced response markers (including IFN-γ, IL-18, IP-10) and inflammatory monocytes activation markers (including MCP-1, IL-1α, IL-1RA) being the main triggers of inflammation. With linear discriminant analysis, MIS-C and KD profiles overlapped; however, a subgroup of MIS-C patients (MIS-C plus ) differentiated from the remaining MIS-C patients in IFNγ, IL-18, GM-CSF, RANTES, IP-10, IL-1α and SDF-1 and incipient signs of macrophagic activation syndrome. Circulating SARS-CoV-2-IC were not detected in MIS-C patients. Our findings suggest a major role of IFN-γ in the pathogenesis of MIS-C, which may be relevant for therapeutic management.

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