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Mucosal antibodies constitute the first line of adaptive immune defence against invaders in the female genital tract (FGT), yet the sequence of events leading to their production is surprisingly poorly characterized. We explored the induction of pathogen-specific antibody-secreting cells (ASC) as a response to an acute infection in the upper FGT. We recruited 12 patients undergoing surgery due to an upper FGT infection (7/12 blood culture positive, 5/ 12 negative) and six healthy controls. Pathogens were sampled during surgery and PBMC collected in the acute phase of the disease (days 7-10). We searched by ELISPOT circulating pathogen-specific ASC and explored their frequency, immunoglobulin isotype distribution, and expressions of homing receptors (alpha(4)beta(7), L-selectin, and CLA). All patients had circulating ASC specific to the infective bacteria; the geometric mean was 434 (95%CI 155-1234) ASC (IgA + IgG + IgM)/10(6) PBMC. IgA ASC predominated in 7/12, IgG ASC in 3/12, and IgM ASC in 2/12 cases. Of all the pathogen-specific ASC, 60% expressed alpha(4)beta(7), 67% L-selectin, and 9% CLA. This study is the first to show induction of pathogen-specific ASC in the peripheral blood in bacterial infection in the human FGT. Our findings reveal that such FGT-originating pathogen-specific ASC are predominated by IgA ASC and exhibit a homing receptor profile resembling that of ASC in acute urinary tract infection. The data thus suggest a characteristic profile shared by the urogenital tract.

Salmonella Typhi is a human host-restricted pathogen that is responsible for typhoid fever in approximately 10.9 million people annually1. The typhoid toxin is postulated to have a central role in disease pathogenesis, the establishment of chronic infection and human host restriction2–6. However, its precise role in typhoid disease in humans is not fully defined. We studied the role of typhoid toxin in acute infection using a randomized, double-blind S. Typhi human challenge model7. Forty healthy volunteers were randomized (1:1) to oral challenge with 104 colony-forming units of wild-type or an isogenic typhoid toxin deletion mutant (TN) of S. Typhi. We observed no significant difference in the rate of typhoid infection (fever ≥38 °C for ≥12 h and/or S. Typhi bacteremia) between participants challenged with wild-type or TN S. Typhi (15 out of 21 (71%) versus 15 out of 19 (79%); P = 0.58). The duration of bacteremia was significantly longer in participants challenged with the TN strain compared with wild-type (47.6 hours (28.9–97.0) versus 30.3(3.6–49.4); P ≤ 0.001). The clinical syndrome was otherwise indistinguishable between wild-type and TN groups. These data suggest that the typhoid toxin is not required for infection and the development of early typhoid fever symptoms within the context of a human challenge model. Further clinical data are required to assess the role of typhoid toxin in severe disease or the establishment of bacterial carriage., Typhoid toxin is not essential for the pathogenesis of typhoid fever in healthy humans challenged with Salmonella Typhi.

Pneumonia is a major cause of death worldwide, with Streptococcus pneumoniae one of the most frequent pathogens [1, 2]. Control of the disease through vaccination has become an objective for preventive health care. The disease begins by the establishment of S. pneumoniae colonization in the upper respiratory tract (URT), followed by descent of the bacteria into the lower respiratory tract (LRT) to bring about a symptomatic infection [1, 2]. Nasopharyngeal carriage is clearly a prerequisite for all S. pneumoniae diseases [2], yet the immunological factors protecting against transition from carriage to disease are not adequately understood. Mucosal antibodies capable of preventing colonization may offer a key approach to protection [3–7]. Indeed, in animal models mucosal vaccines eliciting mucosal antibodies have proved to confer protection against local disease [5, 7, 8]. To develop better vaccination strategies, local immune mechanisms need to be explored in greater detail in humans. Pneumococcal vaccines, either as 23-valent polysaccharide preparations (PPV) or 10- or 13-valent polysaccharide vaccines conjugated to a protein carrier (PCV10 and PCV13, respectively), are licensed in many countries. PPV covers a broader spectrum of serotypes and confers protection against invasive pneumococcal disease, while the efficacy against local, noninvasive pneumonia remains controversial [9–11]. PCVs cover fewer serotypes and are not only effective against invasive pneumococcal disease [12], but also seem to confer some protection against noninvasive pneumonia (efficacy, 20%–37%) [13–15]. The insufficient ability of vaccines to elicit mucosal immune response has been suggested to account for their shortcomings in providing protection against local disease [5]. During an immune response, effector B lymphocytes (plasmablasts) do not spread equally across the body but instead are guided to travel to sites of expected antigen encounter. This tissue-specific homing of lymphocytes from blood into tissues is based on interaction between lymphocyte surface chemokine receptors (CCRs) and homing receptors with chemokines and specific homing receptor-ligands, addressins, on the endothelial cells of the target tissues, respectively [16, 17]. Tissue-specific homing receptors have been identified: L-selectin (CD62L) guides the lymphocytes to the peripheral lymph nodes [18], α4β7-integrin guides lymphocytes to the intestinal lamina propria [19], and cutaneous lymphocyte antigen (CLA) guides lymphocytes to skin tissue [20]. Analysis of the homing receptor and/or CCR profiles of the circulating plasmablasts provides an approach to evaluate the targeting of an immune response elicited at the site of antigen encounter [21–24]. The homing receptors guiding lymphocytes to the LRT have not been identified, but it has been suggested that instead of a single homing receptor, a variety of homing receptors are involved [16, 17, 25]. We have recently detected S. pneumoniae–specific plasmablasts in the circulation of humans with acute pneumococcal pneumonia [26]. These cells are presumed to originate in the LRT and to be responsible for distributing the immune response to various immunological compartments of the body [26]. Exploring these S. pneumoniae–specific plasmablasts allows study of the localization of the immune effector cells of the LRT. Comparing the homing receptor profiles of S. pneumoniae–specific plasmablasts between patients with pneumonia and volunteers who receive parenteral S. pneumoniae vaccines may throw new light on possible differences between natural infection and PPV or PCV in targeting the immune response.

Background Despite the high frequency of upper respiratory tract (URT) infections and use of the nasal mucosa as route for vaccination, the local immune mechanism and dissemination of effector lymphocytes from the URT have been insufficiently characterized. To devise a single-cell approach for studying the mucosal immune response in the URT, we explored URT-originating B effector lymphocytes in the circulation of patients with one of two common respiratory infections, acute sinusitis or tonsillitis. Methods Patients with acute sinusitis (n = 13) or tonsillitis (n = 11) were investigated by ELISPOT for circulating pathogen-specific antibody-secreting cells (ASCs) of IgA, IgG and IgM isotypes approximately one week after the onset of symptoms. These cells' potential to home into tissues was explored by assessing their expression of tissue-specific homing receptors alpha(4)beta(7), L-selectin, and cutaneous lymphocyte antigen (CLA). Results Pathogen-specific ASCs were detected in the circulation of all patients, with a geometric mean of 115 (95% CI 46-282) /10(6) PBMC in sinusitis, and 48 (27-88) in tonsillitis. These responses were mainly dominated by IgG. In sinusitis alpha(4)beta(7) integrin was expressed by 24% of the ASCs, L-selectin by 82%, and CLA by 21%. The proportions for tonsillitis were 15%, 80%, and 23%, respectively. Healthy individuals had no ASCs. Conclusions URT infections-acute sinusitis and tonsillitis-both elicited a response of circulating pathogen-specific plasmablasts. The magnitude of the response was greater in sinusitis than tonsillitis, but the homing receptor profiles were similar. Human nasopharynx-associated lymphoid structures were found to disseminate immune effector cells with a distinct homing profile.

Lower respiratory tract infections (LRTI) are the leading cause of death world-wide, with Streptococcus pneumoniae (Pnc) as the most prevalent pathogen. Local immune mechanisms appear central to protection against the disease, yet they are poorly characterized. Infections at other, non-respiratory mucosal sites are associated with a transient circulation of mucosa-originating lymphocytes from the mucosal site to blood and back to the mucosa. The present study explored whether pathogen-specific plasmablasts appear in the circulation also in patients with infection of the lower respiratory tract. 16 patients with bacteremic Pnc pneumonia and 14 healthy volunteers were explored for circulating plasmablasts secreting antibodies against their own pathogenic Pnc strain isolated in blood cultures (patients) or against several pathogenic strains from pneumonia patients (14 controls) or a mixture of nine different purified pneumococcal polysaccharides (8 controls). Both patients and volunteers were studied for all plasmablasts. The cells were identified with ELISPOT as Pnc-specific antibody-secreting cells (ASC) and as all immunoglobulin-secreting cells (ISC). High numbers of circulating Pnc-specific ASC were found in the acute phase of the disease in all patients with pneumonia (median 97 ASC/10(6) PBMC), but in none of the controls. IgG isotype predominated in 9/16 patients. The numbers of ISC were significantly higher in the patients than in the healthy controls, yet Pnc-specific ASC only accounted for 0.7% of all the patients' ISC.The present study is the first to show that antigen-specific plasmablasts appear in the circulation in pneumonia, suggesting that pulmonary lypmhocytes recirculate in humans. Assessing these cells provides a novel tool for studying immune response to antigens encountered at the LRT.