Role of pulmonary infection in the development of chronic lung disease of prematurity.

We studied the role of ante- and post-natal infection in the development of chronic lung disease (CLD) of prematurity. 192 newborn infants (61 term and 131 pre-term of <34 weeks gestation: 88 with respiratory distress syndrome, 35 developed CLD and eight died) were recruited. 16S ribosomal RNA (rRNA) genes were identified by PCR of DNA isolated from 840 gastric and lung fluid samples. Ureaplasma spp. were also cultured. Presence of 16S rRNA genes (OR 1.6, 95% CI 1.2-2.2) and Ureaplasma spp. (OR 3.6, 95% CI 1.7-7.7) was significantly associated with the development of CLD. This association remained if the 16S rRNA genes and Ureaplasma spp. were first identified within the first 3 days of life (OR 2.4 (95% CI 1.4-4.1) and 3.8 (95% CI 1.4-10.0), respectively) or if first identified after 3 days of age (OR 1.7 (95% CI 1.1-2.8) and OR 5.1 (95% CI 1.3-19.8), respectively). Peak lung fluid interleukin (IL)-6 and IL-8 were significantly associated with presence of microbes (p<0.0001 and p=0.0001, respectively) and development of CLD (p=0.003 and 0.001, respectively). Both early and late microbial presence in neonatal lung fluid samples was significantly associated with the development of CLD suggesting that both ante- and post-natal infection play a role in the development of CLD.

Structure-function studies of the receptors for complement C1q.

C1q is an essential component of the phylogenetically ancient innate complement (C) system and is crucial to our natural ability to ward off infection and clear toxic cell debris (e.g. amyloid fibrils, apoptotic cells). Several candidate C1q receptors [C1q receptor for phagocytosis enhancement (C1qRp), complement receptor (CR) 1, calreticulin (CRT), binding protein for the globular head of C1q (gC1qbp)] have been described, and the aim of this review is to shed light on their structure-function relationships. One cell-surface molecule, C1qRp, has emerged as a defence collagen receptor for C1q, as well as mannose-binding lectin (MBL) and surfactant protein A. C1qRp (also known as the AA4 antigen in rodents) is the antigen recognized by a pro-adhesive monoclonal antibody called mNI-11 and antibodies against CD93, but recent results failed to confirm C1q binding activity. CR1 (CD35), a multifunctional receptor both in its ligand specificity and in its C regulation activities, is found on circulating monocytes and neutrophils, but the major site of expression is B-lymphocytes. As a receptor, CR1 binds to C1q, other C opsonins (C4b, C3b, iC3b) and MBL, and as such, has been involved in promoting phagocytosis. Several studies support a role for the cell surface receptor for the collagenous domains of C1q (cC1qR; also known as CRT). CRT belongs to the family of heat-shock proteins, the most abundant and ubiquitous soluble intracellular proteins. Though CRT does not have a transmembrane domain, it seems to mediate phagocytosis of the apoptotic cells through association with CD91. A 33 kDa protein interacts with the globular head of C1q and, logically, has been termed gC1qbp. This protein is located in mitochondria, suggesting that gC1qbp is not a cell-surface receptor itself.

Endothelial cells, megakaryoblasts, platelets and alveolar epithelial cells express abundant levels of the mouse AA4 antigen, a C-type lectin-like receptor involved in homing activities and innate immune host defense.

Phagocytic complement C1q receptor (C1qRp) and thrombomodulin (TM, CD141), are two key members of a novel family of lectin receptors involved in cell-cell interactions and innate immune host defense. We report here that the mouse homologue of human C1qRp (AA4) and TM are derived from a common ancestor on the basis that both genes co-localized to the same region of the chromosome 2 and also because they share similar domain composition and organization. Moreover, we found that mouse AA4 was localized to sites known to express TM. Mouse AA4 was identified by Western blot as a heavily glycosylated protein (110 kDa) expressed in all tissues tested. Brain and spleen expressed an additional 130-kDa band. Immunoperoxidase and double-immunofluorescence experiments showed that, surprisingly, the major site of AA4 expression in all tissue tested is on endothelial cells and that despite the apparent involvement of AA4 in the phagocytic response, it is not expressed by tissue macrophages. In contrast, megakaryoblasts (in bone marrow and spleen) and platelets expressed abundant levels of AA4 stored in cytoplasmic vesicles. Interestingly, alveolar epithelial cells (lung) but not other epithelia (e.g. uterus) were strongly stained for AA4. Although AA4 has been described on all hematopoietic progenitors, we found that only circulating immature B cells, monocytes and NK cells but not T cells and neutrophils expressed AA4.

Molecular and cellular properties of the rat AA4 antigen, a C-type lectin-like receptor with structural homology to thrombomodulin.

The murine fetal stem cell marker AA4 has recently been cloned and is known to be the homolog of the human phagocytic C1q receptor involved in host defense. We herein report the molecular cloning and the cellular expression pattern of the rat AA4 antigen. Modular architecture analysis indicated that the rat AA4 is a member of C-type lectin-like family and, interestingly, displays similar domain composition and organization to thrombomodulin. Northern blot and reverse transcriptase-polymerase chain reaction analyses indicated that rat AA4 was encoded by a single transcript of 7 kilobases expressed constitutively in all tissues. In situ hybridization showed that AA4 was expressed predominantly by pneumocytes and vascular endothelial cells. Using an affinity purified polyclonal antibody raised against a rat AA4-Fc fusion protein, AA4 was identified as a glycosylated protein of 100 kDa expressed by endothelial cells > platelets > NK cells and monocytes (ED1+ cells). The staining was associated to the cell surface and intracytoplasmic vesicles. Conversely, erythrocytes, T and B lymphocytes, neutrophils, and macrophages (ED2+ cells) were consistently negative for AA4. As expected, the macrophage cell line NR8383 expressed weak levels of AA4. Taken together, our results support the idea that AA4/C1qRp is involved in some cell-cell interactions.

Complement components of the innate immune system in health and disease in the CNS.

The innate immune system and notably the complement (C) system play important roles in host defense to recognise and kill deleterious invaders or toxic entities, but activation at inappropriate sites or to an excessive degree can cause severe tissue damage. C has been implicated as a factor in the exacerbation and propagation of tissue injury in numerous diseases including neurodegenerative disorders. In this article, we review the evidence indicating that brain cells can synthesise a full lytic C system and also express specific C inhibitors (to protect from C activation and C lysis) and C receptors (involved in cell activation, chemotaxis and phagocytosis). We also summarise the mechanisms involved in the antibody-independent activation of the classical pathway of C in Alzheimer's disease, Huntington's disease and Pick's disease. Although the primary role of C activation on a target cell is to induce cell lysis (particularly of neurons), we present evidence indicating that C (C3a, C5a, sublytic level of C5b-9) may also be involved in pro- as well as anti-inflammatory activities. Moreover, we discuss evidence suggesting that local C activation may contribute to tissue remodelling activities during repair in the CNS.