Essential role of neutrophils in the initiation and progression of a murine model of rheumatoid arthritis.

Neutrophils are prominent participants in the joint inflammation of human rheumatoid arthritis (RA) patients, but the extent of their role in the inductive phase of joint inflammation is unknown. In the K/BxN mouse RA model, transfer of autoreactive Ig from the K/BxN mouse into mice induces a rapid and profound joint-specific inflammatory response reminiscent of human RA. We observed that after K/BxN serum transfer, the earliest clinical signs of inflammation in the ankle joint correlated with the presence of neutrophils in the synovial regions of recipient mouse ankle joints. In this study, we investigated the role of neutrophils in the early inflammatory response to transferred arthritogenic serum from the K/BxN transgenic mouse. Mice were treated with a neutrophil-depleting mAb before and following transfer of arthritogenic serum and scored for clinical indications of inflammation and severity of swelling in ankle joints and front paws. In the absence of neutrophils, mice were completely resistant to the inflammatory effects of K/BxN serum. Importantly, depletion of neutrophils in diseased recipient mice up to 5 days after serum transfer reversed the inflammatory reaction in the joints. Transfer of serum into mice deficient in the generation of nitrogen or oxygen radicals (inducible NO synthase 2 or gp91(phox) genes, respectively) gave normal inflammatory responses, indicating that neither pathway is essential for disease induction. These studies have identified a critical role for neutrophils in initiating and maintaining inflammatory processes in the joint.

Trypanosoma cruzi infection does not impair major histocompatibility complex class I presentation of antigen to cytotoxic T lymphocytes.

Trypanosoma cruzi (T. cruzi), the etiological agent of Chagas' disease, lives free within the cytoplasm of infected host cells. This intracellular niche suggests that parasite antigens may be processed and presented on major histocompatibility complex (MHC) class I molecules for recognition by CD8+ T cells. However, the parasite persists indefinitely in the mammalian host, indicating its success at evading immune clearance. It has been shown that T. cruzi interferes with processing and presentation of antigenic peptides in the MHC class II pathway. This investigation sought to determine whether interference in MHC class I processing and presentation occurs with T. cruzi infection. Surface expression of MHC class I molecules was found to be unaffected or up-regulated by T. cruzi infection in vitro. A model system employing a beta-galactosidase (beta-gal)-specific murine cytotoxic T lymphocyte (CTL) line (0805B) showed: (i) in vitro infection of mouse peritoneal macrophages or J774 cells with T. cruzi did not inhibit MHC class I presentation of exogenous peptide (a nine-amino acid epitope of beta-gal) to the CTL line, (ii) in vitro infection of a beta-gal-expressing 3T3 cell line (LZEJ) with T. cruzi did not inhibit MHC class I presentation of the endogenous protein to the CTL line and (iii) mouse renal adenocarcinoma cells infected with T. cruzi and subsequently infected with adenovirus expressing beta-gal were able to present antigen to the beta-gal-specific CTL line. These findings indicate that the failure of the immune response to clear T. cruzi does not result from global interference by the parasite with MHC class I processing and presentation. Parasites engineered to express beta-gal were unable to sensitize infected antigen-presenting cells in vitro to lysis by the CTL 0805B line. This was probably due to the intracellular localization of the beta-gal within the parasite and its inaccessibility to the host cell cytoplasm.

Variable binding affinities of listeriolysin O peptides for the H-2Kd class I molecule.

Previously we used the peptide-binding motif for the murine class I major histocompatibility complex molecule H-2Kd to identify a nonamer peptide of the Listeria monocytogenes listeriolysin (LLO) protein that was recognized by cytotoxic T lymphocytes (CTL) in association with H-2Kd. Eleven nonamer peptides contained in the LLO sequence were synthesized and one, LLO 91-99, proved to be a CTL target. Using peptide binding competition assays with H-2Kd-restricted CTL, we show that 3 out of the 11 LLO peptides, including the CTL epitope, have a high binding affinity for H-2Kd; 2 of 11 peptides have approximately 10-fold lower affinity, while the remaining 6 peptides have no or very low affinity for H-2Kd. Single residue changes were made in the LLO 91-99 peptide and two other LLO peptides to identify non-anchor amino acids that might interfere with peptide binding. In addition, we used the LLO peptides which bound well to H-2Kd to attempt to restimulate a secondary CTL response from L. monocytogenes-primed spleen cells. Only LLO 91-99 was able to induce such a response. Thus only a fraction of nonamer peptides which fit the original binding motif have a high affinity for the H-2Kd class I molecule, and only a fraction of these serve as CTL epitopes.