Rolf M. Zinkernagel

Natural antibodies and complement link innate and acquired immunity

Natural or spontaneous antibodies are an essential part of the first line of defense against hematogenically spreading infections, including viruses. These antibodies target virus-antibody complexes and complement to the spleen. This prevents infections from reaching vital organs and enhances neutralizing antibody responses, particularly when the antibody is bound to a highly repetitive antigen.

FTY720 immunosuppression impairs effector T cell peripheral homing without affecting induction, expansion, and memory.

FTY720 (2-amino-2-(2-[4-octylphenyl]ethyl)-1,3-propanediol hydrochloride) prolongs survival of solid organ allografts in animal models. Mechanisms of FTY720 immunomodulation were studied in mice infected with lymphocytic choriomeningitis virus (LCMV) to assess T cell responses or with vesicular stomatitis virus to evaluate Ab responses. Oral FTY720 (0.3 mg/kg/day) did not affect LCMV replication and specific CTL and B cells were induced and expanded normally. Moreover, the anti-viral humoral immune responses were normal. However, FTY720 treatment showed first a shift of overall distribution of CTL from the spleen to peripheral lymph nodes and lymphocytopenia was observed. This effect was reversible within 7–21 days. Together with unimpaired T and B cell memory after FTY720 treatment, this finding rendered enhancement of lymphocyte apoptosis by FTY720 in vivo unlikely. Secondly, the delayed-type hypersensitivity reaction to a viral MHC class I-presented peptide was markedly reduced by FTY720. These results were supported by impaired circulation of LCMV specific TCR transgenic effector lymphocytes in the peripheral blood and reduced numbers of tissue infiltrating CTL in response to delayed-type hypersensitivity reaction. Thirdly, in a CD8+ T cell-mediated diabetes model in a transgenic mouse expressing the LCMV glycoprotein in the islets of the pancreas, FTY720 delayed or prevented disease by reducing islet-infiltrating CTL. Thus, FTY720 effectively reduced recirculation of CD8+ effector T cells and their recruitment to peripheral lesions without affecting the induction and expansion of immune responses in secondary lymphoid organs. These properties may offer the potential to treat ongoing organ-specific T cell-mediated immunopathologic disease.

Targeted Inactivation of the Tetraspanin CD37 Impairs T-Cell-Dependent B-Cell Response under Suboptimal Costimulatory Conditions

ABSTRACT CD37 is a membrane protein of the tetraspanin superfamily, which includes CD9, CD53, CD63, CD81, and CD82. Many of these molecules are expressed on leukocytes and have been implicated in signal transduction, cell-cell interactions, and cellular activation and development. We generated and analyzed mice deficient for CD37. Despite the high expression of CD37 on cells of the immune system, no changes in development and cellular composition of lymphoid organs were observed in mice lacking CD37. Analyses of humoral immune responses revealed a reduced level of immunoglobulin G1 (IgG1) in the sera of nonimmunized mice and an alteration of responses to T-cell-dependent antigens. Antibody responses to model antigen administered in the absence of adjuvant and to viral infections were generally poor in CD37-deficient mice. These poor antibody responses could be overcome by the immunization of antigen together with adjuvant. These results suggest a role for CD37 in T-cell–B-cell interactions which manifests itself under suboptimal costimulatory conditions.

In vivo antigen loading and activation of dendritic cells via a liposomal peptide vaccine mediates protective antiviral and anti-tumour immunity

Initiation of antiviral and anti-tumour T cell responses is probably achieved mainly by dendritic cells (DC) transporting antigen from the periphery into organised lymphoid tissues. To develop T cell vaccines it is, therefore, important to understand the accessibility of the antigen to DC in vivo and whether DC are activated by vaccination. Here we have evaluated the immunogenicity of a liposomal vaccine formulation with antigenic peptides derived from the glycoprotein of the lymphocytic choriomeningitis virus. Liposome-encapsulated peptides were highly immunogenic when administered intradermally and elicited protective antiviral immunity. After intradermal injection, liposomes formed antigen depots which facilitated long-lasting in vivo antigen loading of dendritic cells almost exclusively in the local draining lymph nodes. The immunogenicity of the liposomal peptide vaccine was further enhanced by incorporation of immunostimulatory oligonucleotides leading to activation of DC. This optimised liposomal peptide vaccine elicited also anti-tumour immunity and induced CTL responses comparable to adoptively transferred, peptide-presenting DC. Thus, our data show that liposomal formulations of peptide vaccines are highly effective at direct in vivo antigen loading and activation of DC leading to protective antiviral and anti-tumour immune responses.

Direct quantitation of rapid elimination of viral antigen-positive lymphocytes by antiviral CD8 + T cells in vivo

Lysis of infected cells by CD8+ T cells is an important mechanism for the control of virus infections, but remains difficult to quantify in vivo. Here, we study the elimination kinetics of viral antigen‐positive lymphocytes by antiviral CD8+ T cells using flow cytometry and mathematical analysis. In mice acutely infected with lymphocytic choriomeningitis virus, more than 99.99u2009% of target cells were eliminated each day, corresponding to a half‐life of 1.4u2004h. Even in mice exposed to virus 300 days previously, and with no ex vivo killing activity, 84u2009% of the target cells were eliminated per day. Unexpectedly, the elimination kinetics of antigen‐positive lymphocytes was not significantly impaired in mice deficient in either perforin‐, CD95 ligand‐ or TNF‐mediated cytotoxicity. For viruses with a particular tropism for lymphocytes, such as Epstein‐Barr virus or HIV, our results illustrate how effectively CD8+ T cell‐mediated elimination of target cells can potentially contribute to virus control and immunosuppression.

What is missing in immunology to understand immunity

The question of how we acquire immunity has been investigated for a century or more. What have we learned from all of this endeavor? We asked Rolf Zinkernagel to provide, for the young investigator, food for thought about that which we still dont know—even if we think we do.

Correlation of T cell independence of antibody responses with antigen dose reaching secondary lymphoid organs: implications for splenectomized patients and vaccine design.

Many natural viral and bacterial pathogens activate B cells independently of Th cells (TI Ags). This study analyzed the characteristics of the activation of B cells after immunization with various forms of viral Ags using different immunization routes and found a decreasing dependence on T help with increasing amounts of Ag recruited to the spleen. Repetitive antigenic structure facilitated TI B cell responses if Ag was present in lymphoid organs. These results suggest that 1) Ag dose and localization in secondary lymphoid organs are the key for B cell activation in the absence of T help; 2) early TI Ab responses are crucial to protect against systemically spreading acute cytopathic infectious agents; and 3) there may be new rationales for improved vaccine design.

Induction of optimal anti-viral neutralizing B cell responses by dendritic cells requires transport and release of virus particles in secondary lymphoid organs

Dendritic cells (DC) are sentinels of the immune system, transporting antigens from the periphery to secondary lymphoid organs. This study investigates the interactions of DC with B cells for the induction of anti‐viral neutralizing antibody responses. Using the vesicular stomatitis virus glycoprotein (VSV‐G) as a model antigen, we show that DC contain infection with cytopathic VSV in the presence of a functional IFN system, facilitating transport and release of low levels of live virus in secondary lymphoid organs. DC exposed to live virus induced efficient neutralizing anti‐viral B cell responses. In contrast, DC transporting UV‐inactivated viral antigens were poor activators of anti‐viral B cells, although they were capable of very efficiently inducing virus‐specific Th cells. Transgenic DC expressing a membrane‐bound form of VSV‐G induced neutralizing B cell responses; however, this DC‐induced, Th‐dependent B cell response was significantly slower than the anti‐viral B cell response induced by DC infected with live VSV, and was strongly dependent on concomitant priming of T help. These results suggest that DC may play a double role during infection with cytopathic virus: they transport and release live virus in secondary lymphoid tissues for optimal direct B cell induction and offer MHC class II‐associated determinants for induction of T help.

On immunological memory.

Immunological memory is a hallmark of the immune system. Evolution can teach us which effector arms of immunological memory are biologically relevant against which virus. Antibodies appear to be the critical protective mechanism against cytopathic viruses. Since these viruses cause cell damage and disease directly, particularly in the absence of an immune response, mothers protect their offspring during a critical immunoincompetent period (a consequence of MHC- restricted T cell recognition) by passive transfer of neutralizing antibodies. In contrast, CTL appear to be the crucial effector mechanism against noncytopathic viruses. Since MHC polymorphism has made vertical transmission of T cell memory impossible, immunoincompetent offspring are not, and need not be, protected against such noncytopathic viruses. During the primary response and again during secondary infection, the most important function of CTL is to eliminate noncytopathic viruses, which may otherwise cause lethal immunopathology. Increased precursor frequencies of B and T cells appear to remain in the host independent of antigen persistence. However, in order to protect against cytopathic viruses, memory B cells have to produce antibody to maintain protective elevated levels of antibody; B cell differentiation into plasma cells is driven by persisting antigen. Similarly, to protect against infection with a noncytopathic virus, CTL have to recirculate through peripheral organs. Activation and capacity to emigrate into solid tissues as well as cytolytic effector function are also dependent upon, and driven by, persisting antigen. Because no convincing evidence is available yet of the existence of identifiable B or T cells with specialized memory characteristics, the phenotype of immunological memory correlates best with antigen-driven activation of low frequency effector T cells and plasma cells.

Immunodeficiency of alymphoplasia mice (aly/aly) in vivo: structural defect of secondary lymphoid organs and functional B cell defect

Alymphoplasia mice (aly/aly) have been shown to be deficient for a nuclear factor‐κB‐inducing kinase involved in signal transduction of lymphotoxin β receptor (LT‐βR) and of CD40, resulting in structural defects of secondary lymphoid organs and highly increased susceptibility to viral infections. We analyzed the anti‐viral immune response of bone marrow chimeras (BMC) between aly/aly mice and (C57BL/6 × DBA2)F1 mice (B6D2F1) to evaluate in vivo whether the structural defects of secondary lymphoid organs or intrinsic B or T cell defects led to immunodeficiency in aly/aly mice. Transfer of aly/aly bone marrow into B6D2F1 mice (aly/aly→B6D2F1) led to excellent T but poor B cell reconstitution of recipients. Antiviral cytotoxic T cell (CTL) responses of aly/aly→B6D2F1 BMC were clearly improved compared to aly/aly mice whereas virus‐neutralizing IgG reponses were virtually absent. Therefore, the inefficient CTL response was predominantly caused by the structural defect of secondary lymphoid organs and not by an intrinsic T cell defect. In contrast, B cells of aly/aly origin were unable to undergo isotype switch after viral infections, indicating an intrinsic B cell defect in vivo. Overall, aly/aly mice show the combined immunodeficient phenotype of mice deficient for LT‐βR with B cells functionally deficient for CD40.