Protective anti-Helicobacter immunity is induced with aluminum hydroxide or complete Freund's adjuvant by systemic immunization.

To determine whether systemic immunization against Helicobacter pylori could be achieved with an adjuvant approved for human use, the efficacy of vaccination with Helicobacter antigen in combination with aluminum hydroxide (AlOH) was evaluated in a murine model of Helicobacter infection. Immunization with antigen and AlOH induced interleukin-5-secreting, antigen-specific T cells, and immunization with antigen and complete Freund's adjuvant induced interferon-gamma-secreting, antigen-specific T cells, as determined by ELISPOT assay. Both immune responses conferred protection after challenge with either H. pylori or H. felis, as confirmed by the complete absence of any bacteria, as assessed by both histology and culture of gastric biopsy samples. Protection was antibody independent, as demonstrated with antibody-deficient muMT mice (immunoglobulin-gene knockout mice), and CD4(+) spleen T cells from immunized mice were sufficient to transfer protective immunity to otherwise immunodeficient rag1(-/-) recipients. These results suggest an alternative and potentially more expeditious strategy for development of a human-use H. pylori vaccine.

Frequencies of neuroantigen-specific T cells in the central nervous system versus the immune periphery during the course of experimental allergic encephalomyelitis.

Direct measurements of the frequency and the cytokine signature of the neuroantigen-specific effector cells in experimental allergic encephalomyelitis (EAE) are a continuing challenge. This is true for lymphoid tissues, and more importantly, for the CNS itself. Using enzyme-linked immunospot analysis (ELISPOT) assays, we followed proteolipid protein (PLP) 139--151-specific T cells engaged by active immunization of SJL mice. The total numbers of PLP(139--151)-specific CD4 cells were highest before disease onset. At this time, these cells resided in lymphoid and nonlymphoid tissues, but were not detected in the CNS. While the PLP(139--151)-specific cells reached high frequencies in the CNS during clinical EAE, in absolute numbers, less than 20% of them were present in the target organ, with the majority residing in the periphery throughout all stages of the disease. The numbers of PLP(139--151)-specific cells gradually declined in both compartments with time. While eventually this first wave of effector cells completely disappeared from the CNS, PLP(178--191)-specific cells became engaged, being detected first in the CNS. These data suggest that throughout all stages of EAE, the effector cells in the CNS are recruited from a vast peripheral reservoir, and that the second wave of effector cells is engaged while the first wave undergoes exhaustion.

Prevention of murine EAE by oral hydrolytic enzyme treatment.

Clinical trials that test the efficacy of Phlogenzym (consisting of the hydrolytic enzymes bromelain and trypsin and the anti-oxidant rutosid) as a treatment for T cell-mediated autoimmune diseases including multiple sclerosis (MS), type 1 diabetes and rheumatoid arthritis are presently ongoing. We tested the effects of Phlogenzym treatment in the murine model for MS, experimental allergic encephalomyelitis (EAE), a disease induced in SJL mice by immunization with proteolipid protein (PLP) peptide 139-151. Oral administration of Phlogenzym resulted in complete protection from EAE. In Phlogenzym-treated mice, the dose response curve of the PLP:139-151-specific T cell response was shifted to the right, that is, the primed T cells required higher peptide concentrations to become activated. Additionally, the T cell response to this peptide was shifted towards the T helper 2 cytokine profile. Both effects are consistent with an increased T cell activation threshold. In support of this interpretation, we found that the accessory molecules CD4, CD44, and B7-1 (all of which are involved in T cell co-stimulation) were cleaved by Phlogenzym, while CD3 and MHC class II molecules (which are involved in the recognition of antigens by T cells) and LFA-1 were unaffected. These data show the efficacy of oral Phlogenzym treatment in an animal model of T cell-mediated autoimmune disease and suggest that the protective effect might be the result of an increase in the activation threshold of the autoreactive T lymphocytes brought about by the cleavage of accessory molecules involved in the interaction of T cells and antigen presenting cells.

Shifting T-cell activation thresholds in autoimmunity and determinant spreading.

The best-characterized autoimmune T-cell response is that to myelin basic protein (MBP). MBP has classically been regarded as a sequestered antigen that does not cause negative selection. This view has been fostered by the observation that T-cell receptor-transgenic T cells that are specific for the "immunodominant determinant" on the molecule, MBP:Ac1-11, persist as naive cells in MBP-expressing H-2u mice. The same T cells, however, can cause autoimmune pathology once they have been primed by environmental stimulation to become memory cells. Once the autoimmune response to Ac1-11 has been engaged, determinant spreading occurs and second-wave T-cell responses that are specific for weaker, "cryptic" determinants like MBP:121-140 develop. Although the nature of these cryptic determinants has been enigmatic, recent studies using MBP-/- mice have provided new insights. These studies showed that MBP is not a sequestered antigen, but one that causes negative selection; as MBP:121-140 is actually the immunodominant determinant in MBP-/- mice, it tolerizes high avidity clones in MBP+/+ mice, making it appear cryptic. Based on this new information, we attempt here to redefine the MBP-specific repertoire within the theoretical framework of the threshold model for negative selection, and we propose a model of shifting T-cell activation thresholds to explain how ignorant/naive T cells can become effector cells of autoimmune pathology and why this effector cell repertoire spreads.

Endogenous myelin basic protein inactivates the high avidity T cell repertoire.

To study the contribution of endogenous myelin basic protein (MBP) to the positive and/or negative selection of the MBP-specific T cell repertoire, we studied the T cell response to MBP in MBP-deficient shiverer and MBP-expressing congenic C3H mice. Immunization with MBP induced a vigorous T cell response in shiverer mice directed against a single I-Ak- restricted immunodominant determinant, the core of which is peptide MBP:79-87 (DENPVVHFF). Injection of this peptide induced a high avidity T cell repertoire in shiverer mice that primarily consisted of clones capable of recognizing the native MBP protein in addition to the peptide itself. These data show that endogenous MBP is not required for the positive selection of an MBP-specific T cell repertoire. C3H mice, in contrast, were selectively unresponsive to the MBP protein and injection of MBP:79-87 peptide induced a low avidity repertoire that could be stimulated only by the peptide, not by the protein. Therefore, endogenous MBP induced profound inactivation of high avidity clones specific for the immunodominant determinant making that determinant appear cryptic.

CpG oligodeoxynucleotides act as adjuvants that switch on T helper 1 (Th1) immunity.

Synthetic oligodeoxynucleotides (ODN) that contain unmethylated CpG motifs (CpG ODN) induce macrophages to secrete IL-12, which induces interferon (IFN)-gamma secretion by natural killer (NK) cells. Since these cytokines can induce T helper 1 (Th1) differentiation, we examined the effects of coadministered CpG ODN on the differentiation of Th responses to hen egg lysozyme (HEL). In both BALB/c (Th2-biased) and B10.D2 (Th1-biased) mice, immunization with HEL in incomplete Freund's adjuvant (IFA) resulted in Th2-dominated immune responses characterized by HEL-specific secretion of IL-5 but not IFN-gamma. In contrast, immunization with IFA-HEL plus CpG ODN switched the immune response to a Th1-dominated cytokine pattern, with high levels of HEL-specific IFN-gamma secretion and decreased HEL-specific IL-5 production. IFA-HEL plus CpG ODN also induced anti-HEL IgG2a (a Th1-associated isotype), which was not induced by IFA-HEL alone. Control non-CpG ODN did not induce IFN-gamma or IgG2a, excepting lesser increases in B10.D2 (Th1-biased) mice. Thus, CpG ODN provide a signal to switch on Th1-dominated responses to coadministered antigen and are potential adjuvants for human vaccines to elicit protective Th1 immunity.