T cell response to myoglobin: a comparison of T cell clones in high-responder and low-responder mice

The F(ab′)2 fragment of an Aβ-specific monoclonal antibody reduces Aβ deposits in the brain

This work examines whether administering the F(ab' )2 fragment of an IgG1 monoclonal antibody (mAb) targeting the N-terminal 1-13 amino acids of the beta-amyloid peptide (Abeta mAb) reduces amyloid deposition in Alzheimer's disease (AD). The F(ab')2 fragment was injected intraperitoneally or intracranially into Tg2576 mice, a murine model of human AD. Both routes of administration significantly reduced Abeta plaque formation in the brain, as determined immunohistochemically and by monitoring levels of Abeta1-40 and Abeta1-42 peptide. Use of the F(ab')2 fragment significantly reduced phagocytic infiltration in the CNS when compared to intact mAb. Since IgG1 Abs do not fix complement, these findings suggest that effective in vivo clearance of amyloid deposits can be achieved without stimulation of FcR-reactive phagocytes or activation of the complement cascade.

Human immunodeficiency virus type-1-specific immune responses induced by DNA vaccination are greatly enhanced by mannan-coated diC14-amidine

Use of mannan-coated N-t-butyl-N'-tetradecyl-3-tetradecylamino-propionamidine (diC14-amidine) as an adjuvant for a DNA vaccine encoding glycoprotein 160 of human immunodeficiency virus type-1 (HIV-1) enhanced the antigen-specific immune responses. The role of interferon-gamma (IFN-gamma) and interleukin-12 in the mechanism of adjuvant action was also evaluated. Coating of diC14-amidine with mannan significantly augmented the HIV-specific delayed-type hypersensitivity reaction induced by the immunogenic DNA. HIV-1-specific cytotoxic T lymphocyte activity was also markedly enhanced by the mannan-diC14-amidine cocktail. An immunomodulatory effect of this cocktail was inhibited by treatment with anti-IFN-gamma monoclonal antibody in vivo, which suggests that IFN-gamma plays an important role in inducing cell-mediated immunity by the DNA vaccine containing this adjuvant. The results of both antigen-specific immunoglobulin isotype analysis and cytokine measurement showed that the immunogenic DNA incorporated into mannan-coated diC14-amidine elicits Th1-biased immune responses.

Cationic liposomes are a strong adjuvant for a DNA vaccine of human immunodeficiency virus type 1

Liposomes have been widely used to enhance the immune response. In the present investigation, we studied their in vivo immunomodulation of an HIV-1-specific DNA vaccine candidate (pCMV160/REV) constructed with the cytomegalovirus (CMV) promoter-conjugated HIV-1 env and rev DNA plasmids. By immunizing with pCMV160/REV and cationic liposomes through various routes (intramuscular, intraperitoneal, subcutaneous, intradermal, and intranasal), we induced higher levels of both antibody production and delayed-type hypersensitivity (DTH) than by using DNA vaccine alone. The HIV-1-specific cytotoxic T lymphocyte (CTL) activity was observed to be stronger on immunization with the DNA vaccine and cationic liposome combination. The intramuscular, intraperitoneal, and intranasal inoculation routes were more effective in inducing strong DTH and antibody responses than the subcutaneous and intradermal routes. Taken together, these results suggest that cationic liposomes can be highly effective when used with DNA vaccines and administered by various routes.

Relative susceptibility of SJL/J and B10.S mice to experimental allergic encephalomyelitis is correlated with high and low responsiveness to myelin basic protein

SJL/J mice are highly susceptible to actively induced experimental allergic encephalomyelitis (EAE), whereas B10.S mice are not. Yet both strains share the H-2s major histocompatibility complex (MHC) haplotype. In order to help determine the cellular basis for the disparate susceptibility to EAE, the antigen-specific in vitro proliferative responses of lymph node (LN) T cells from SJL/J and B10.S mice primed with porcine myelin basic protein (MBP) were assessed. The results indicated that SJL/J mice were high responders and B10.S mice were low responders to both porcine and murine MBP, as demonstrated by limiting dilution analyses and cloning efficiency analysis of MBP-reactive T cells. The low response of B10.S mice to MBP was not due to elevated suppressor cell activity or to a discernible defect in antigen-presenting cell activity. Rather, it appeared to be due to a paucity (or defect in function) of high affinity MBP-reactive T cells in B10.S as compared to SJL/J mice. This difference in MBP responsiveness must, by necessity, be linked to non-MHC background genes. Therefore, assuming that the relative number of MBP-reactive T cells parallels that of EAE-effector T cells in SJL/J and B10.S mice (as separate in vivo studies indicate), the present results suggest that differences in the T cell repertoire for the encephalitogenic determinants of MBP may contribute significantly to the observed differences in antigen reactivity, and may relate to differences in susceptibility to EAE.

Antigen processing by endosomal proteases determines which sites of sperm-whale myoglobin are eventually recognized by T cells

This study reports an identification of the major processing products of an exogenous protein antigen, viz, sperm-whale myoglobin, as obtained after cell-free processing with partially purified macrophage endosomes. It is demonstrated that such a system yields fragments that are indistinguishable by high performance liquid chromatography analysis from those generated after uptake of myoglobin inside live macrophages. The concerted action of the endosomal proteases cathepsin D and cathepsin B can account for nearly all cleavages observed. Cathepsin D appears to be mainly responsible for the initial cleavage of myoglobin, while cathepsin B catalyzes the C-terminal trimming of initially released fragments. The fragments released by cathepsin D contain most, if not all, major epitopes for murine myoglobin-specific helper T cells. Interestingly, each known T cell epitope of myoglobin is located at the very N terminus of a different myoglobin fragment released upon processing. In order to explain this correspondence, noted also in several other protein antigens, a structural relationship is proposed between antigen processing by cathepsin D and antigen recognition by major histocompatibility complex (MHC) class II products. As is demonstrated here, this relationship may be used as a predictive tool for the identification of MHC-binding sequences as well as of T cell epitopes in their naturally occurring form.

Autoimmune T cell recognition of human acetylcholine receptor: the sites of T cell recognition in myasthenia gravis on the extracellular part of the alpha subunit

Autoimmune T cell lines were prepared from peripheral blood lymphocytes of five myasthenia gravis patients by passage in vitro with an equimolar mixture of 18 overlapping synthetic peptides corresponding to the entire extracellular region (residues alpha 1-210) of the alpha subunit of human acetylcholine receptor (AChR). The proliferative responses of the human AChR-specific T cell lines to each of the individual peptides were determined. It was found that the profiles of the peptides recognized by the T cells were different among the five T cell lines, consistent with genetic control operating at the recognition site level. However, other regulatory influences may play important roles in the triggering of the autoimmune responses. These results suggest that the pathogenesis of this autoimmune disease is variable at the cellular-molecular level.

Genetic control of contact photosensitivity to tetrachlorosalicylanilide. I. Preferential activation of suppressor T cells in low responder H-2k mice

The genetic control of contact photosensitivity (CPS) to 3,3',4',5-tetrachlorosalicylanilide (TCSA) was studied in H-2- and IgH-congenic mice. The H-2 complex was found to play a major role in determining the pattern of responsiveness, whereas the effect of the Igh locus on the response was not apparent. The H-2k haplotype was closely associated with low responders, whereas mice with the H-2b,d alleles were high responders. The responsiveness of the H-2k strains was converted from low to high levels by treatment with cyclophosphamide (CY) before photosensitization. Transfer of spleen cells from photosensitized H-2k mice showed a suppressive effect on the development of the CPS reaction of syngeneic recipients pretreated with CY. These spleen cells contained antigen-specific CD4+, CD8- suppressor T cells (Ts) that functioned in the induction phase of CPS. The in vitro proliferation of immune lymph node T cells pulsed with photohapten-coupled cells plus peritoneal adherent cells was suppressed by the addition of anti-I-A monoclonal antibody in both H-2d and H-2k strains, suggesting that the I-A molecule are responsible for inducing the positive immune response. On the other hand, such proliferation was significantly enhanced by the addition of anti-I-E alpha antibody in H-2k, but not H-2d, mice. This implies that the low responsiveness of CPS in the H-2k strain is due to the preferential activation of Ts via I-Ek molecules. The present observation further supports the important role of the I-E molecule in the suppressor circuit of CPS to TCSA.

Mapping of the full profile of T cell allorecognition regions on HLA-DR2 beta subunit

Alloreactive human T cell lines were developed by repeated in vitro restimulation with alternate allogeneic cells of similar DR2 serotype, but differing at other HLA loci. These polyclonal T cells recognized DR specificities in common with all DR2 serotypes. The allorecognition profiles of DR2 beta by the T cell lines were mapped by consecutive uniform-sized overlapping peptides encompassing the entire extracellular and intracellular regions of the DR beta subunit. It was found that the T cell allorecognition sites are focused around the first and third polymorphic regions of the N-terminal domain, and interestingly, include conserved areas in the DR beta second domain as well as the intracellular segment beta 222-237. These findings have important implications for allorecognition. Comparison with the previous analysis of antibody-binding regions of DR2 beta revealed some similarities and differences in the antibody and T cell alloresponses to this histocompatibility antigen.