Human B- and T-cell responses after immunization with a hexavalent PorA meningococcal outer membrane vesicle vaccine.

The PorA protein from Neisseria meningitidis, a potential vaccine candidate, induces human bactericidal antibodies which are serosubtype specific. We developed a hexavalent PorA outer membrane vesicle vaccine based on reference strain H44/76. This vaccine contains the six most prevalent PorA serosubtypes as found in many countries. We previously reported on the immune responses of 20 adult volunteers after a single immunization with this vaccine. In this study, the B- and T-cell responses in three adult volunteers were studied after three consecutive immunizations (0, 2, and 11 months). The first immunization induced a strong B-cell response resulting in high immunoglobulin G levels in an outer membrane vesicle enzyme-linked immunosorbent assay. At least a fourfold increase in bactericidal activity was observed against the majority (four to six) of the vaccine antigens compared to prevaccination titers. Immunodominance was observed for one or two of the PorAs in the bactericidal assay with a set of six isogenic H44/76-derived PorA target strains. These strains carry the individual PorAs as present in the vaccine. The second and third immunizations did not induce a further increase in the immune responses. A decline in time with respect to PorA-specific antibodies was observed after each immunization. These observations were reflected by the T-cell proliferation responses. Two additional sets of isogenic H44/76-derived mutant strains were used to study the specificity and/or cross-reactivity of the induced bactericidal antibodies. These target strains differ only in expressing mutant family variants of either PorA P1.7,16 or P1.5,10, both present in the PorA vesicle vaccine. The bactericidal antibody responses found were directed predominantly against the P1.7 (loop 1 of P1.7,16) and the P1.10 (loop 4 of P1.5,10) epitopes. This indicates that different portions of PorA were involved in the induction of bactericidal antibodies depending upon the PorA serosubtype.

Specificity of human bactericidal antibodies against PorA P1.7,16 induced with a hexavalent meningococcal outer membrane vesicle vaccine.

A set of isogenic strains was constructed from the meningococcal reference strain H44/76 (B:15:P1.7,16) which differed only in their outer membrane protein (OMP) compositions. First, three isogenic strains lacking the expression of either class 3 (PorB) or class 4 (RmpM) OMP or both were obtained. Second, three isogenic class 1 OMP loop-deficient strains of H44/76 lacking the predicted loop 1 or 4 or both of class 1 OMP (PorA) were obtained. Third, three isogenic class 1 OMP strains which differed by point mutations in the predicted loop 4 of subtype P1.16 were constructed. Strains were constructed through transformation with gene constructs made in Escherichia coli and their homologous recombination into the meningococcal chromosome. This study describes the contribution of one of the six class 1 OMPs, PorA P1.7,16, in the development of bactericidal antibodies after a single immunization of adult volunteers with 50 or 100 micrograms of protein within a hexavalent PorA outer membrane vesicle vaccine. PorA-, PorB-, and RpmM-deficient isogenic strains were used to define the human immune response against PorA. The loop-deficient isogenic strains were used to define the contribution of loops 1 and 4 of PorA in the development of bactericidal anti-PorA antibodies. The isogenic strains carrying a point mutation in loop 4 were used to study the cross-reactivity of the induced bactericidal antibodies against target strains showing microheterogeneity. The results indicate that a single immunization with the hexavalent PorA vaccine induced a dose-dependent bactericidal immune response, which is directed mainly against PorA. The epitope specificity of antibodies is directed mostly against loop 1, although loop 4 and as-yet-unidentified epitopes of PorA P1.7,16 are also involved.

Therapeutic effect of the D2-dopamine agonist bromocriptine on acute and relapsing experimental allergic encephalomyelitis.

We examined the effect of bromocriptine (BCR) treatment on the duration and severity of neurological symptoms of acute experimental allergic encephalomyelitis (EAE), an animal model for demyelinating diseases, particularly multiple sclerosis. To mimic the clinical situation, BCR treatment was started after the onset of clinical signs. Furthermore, the effect of BCR treatment on the course of a chronic relapsing form of EAE was studied. BCR was injected at daily intervals in a dose that resulted in sustained suppression of plasma concentrations of prolactin, a pituitary hormone that plays a role in immunoregulation. In acute EAE, BCR therapy reduced both severity and duration of the clinical signs. In chronic relapsing EAE, BCR treatment did not affect the severity and duration of the first attack, but reduced the duration of the subsequent, second attack. Thus, BCR treatment improves the clinical course in animals with ongoing disease. These findings may have implications for the search for new therapeutic approaches in multiple sclerosis.