Ricci Susanna, Gerlini Alice, Pammolli Andrea, Chiavolini Damiana, Braione Velia, Tripodi Sergio Antonio, Colombari Bruna, Blasi Elisabetta, Oggioni Marco Rinaldo, Peppoloni Samuele, Pozzi Gianni
Department of Medical Biotechnologies, Laboratory of Molecular Microbiology and Biotechnology (LA,M,M,B,), University of Siena and Siena University Hospital, Siena 53100, Italy.
BMC Infect Dis. 2013 Sep 24;13:444. doi: 10.1186/1471-2334-13-444.
Pneumococcal meningitis (PM) is a life-threatening disease with a high case-fatality rate and elevated risk for serious neurological sequelae. In this study, we investigated the contribution of three major virulence factors of Streptococcus pneumoniae, the capsule, pneumococcal surface protein A (PspA) and C (PspC), to the pathogenesis of experimental PM.
Mice were challenged by the intracranial route with the serotype 4 TIGR4 strain (wt) and three isogenic mutants devoid of PspA, PspC, and the capsule. Survival, bacterial counts, and brain histology were carried out. To study the interaction between S. pneumoniae mutants and microglia, phagocytosis and survival experiments were performed using the BV2 mouse microglial cell line.
Virulence of the PspC mutant was comparable to that of TIGR4. In contrast, survival of animals challenged with the PspA mutant was significantly increased compared with the wt, and the mutant was also impaired at replicating in the brain and blood of infected mice. Brain histology indicated that all strains, except for the unencapsulated mutant, caused PM. Analysis of inflammation and damage in the brain of mice infected with TIGR4 or its unencapsulated mutant demonstrated that the rough strain was unable to induce inflammation and neuronal injury, even at high challenge doses. Results with BV2 cells showed no differences in phagocytic uptake between wt and mutants. In survival assays, however, the PspA mutant showed significantly reduced survival in microglia compared with the wt.
PspA contributed to PM pathogenesis possibly by interacting with microglia at early infection stages, while PspC had limited importance in the disease. The rough mutant did not cause brain inflammation, neuronal damage or mouse death, strengthening the key role of the capsule in PM.
肺炎球菌性脑膜炎（PM）是一种危及生命的疾病，病死率高，发生严重神经后遗症的风险增加。在本研究中，我们调查了肺炎链球菌的三种主要毒力因子，即荚膜、肺炎球菌表面蛋白A（PspA）和C（PspC）在实验性PM发病机制中的作用。
通过颅内途径用4型TIGR4菌株（野生型）和三种缺乏PspA、PspC和荚膜的同基因突变体对小鼠进行攻击。进行了生存、细菌计数和脑组织学检查。为了研究肺炎链球菌突变体与小胶质细胞之间的相互作用，使用BV2小鼠小胶质细胞系进行了吞噬作用和生存实验。
PspC突变体的毒力与TIGR4相当。相比之下，用PspA突变体攻击的动物的存活率与野生型相比显著提高，并且该突变体在感染小鼠的脑和血液中复制也受到损害。脑组织学表明，除无荚膜突变体外，所有菌株均引起PM。对感染TIGR4或其无荚膜突变体的小鼠脑内炎症和损伤的分析表明，即使在高攻击剂量下，粗糙菌株也无法诱导炎症和神经元损伤。BV2细胞的结果显示野生型和突变体之间的吞噬摄取没有差异。然而，在生存试验中，与野生型相比，PspA突变体在小胶质细胞中的存活率显著降低。
PspA可能通过在感染早期与小胶质细胞相互作用而促进PM发病机制，而PspC在该疾病中的重要性有限。粗糙突变体未引起脑炎症、神经元损伤或小鼠死亡，这强化了荚膜在PM中的关键作用。
