GENETIC CONTROL OF THE ANTIBODY RESPONSE IN INBRED RATS

A novel vaccine platform using glucan particles for induction of protective responses against Francisella tularensis and other pathogens

Vaccines are considered the bedrock of preventive medicine. However, for many pathogens, it has been challenging to develop vaccines that stimulate protective, long-lasting immunity. We have developed a novel approach using β-1,3-D-glucans (BGs), natural polysaccharides abundantly present in fungal cell walls, as a biomaterial platform for vaccine delivery. BGs simultaneously provide for receptor-targeted antigen delivery to specialized antigen-presenting cells together with adjuvant properties to stimulate antigen-specific and trained non-specific immune responses. This review focuses on various approaches of using BG particles (GPs) to develop bacterial and fungal vaccine candidates. A special case history for the development of an effective GP tularaemia vaccine candidate is highlighted.

Protection induced by a Francisella tularensis subunit vaccine delivered by glucan particles

Francisella tularensis is an intracellular pathogen causing the disease tularemia, and an organism of concern to biodefence. There is no licensed vaccine available. Subunit approaches have failed to induce protection, which requires both humoral and cellular immune memory responses, and have been hampered by a lack of understanding as to which antigens are immunoprotective. We undertook a preliminary in silico analysis to identify candidate protein antigens. These antigens were then recombinantly expressed and encapsulated into glucan particles (GPs), purified Saccharomyces cerevisiae cell walls composed primarily of β-1,3-glucans. Immunological profiling in the mouse was used to down-selection to seven lead antigens: FTT1043 (Mip), IglC, FTT0814, FTT0438, FTT0071 (GltA), FTT0289, FTT0890 (PilA) prior to transitioning their evaluation to a Fischer 344 rat model for efficacy evaluation. F344 rats were vaccinated with the GP protein antigens co-delivered with GP-loaded with Francisella LPS. Measurement of cell mediated immune responses and computational epitope analysis allowed down-selection to three promising candidates: FTT0438, FTT1043 and FTT0814. Of these, a GP vaccine delivering Francisella LPS and the FTT0814 protein was able to induce protection in rats against an aerosol challenge of F. tularensis SchuS4, and reduced organ colonisation and clinical signs below that which immunisation with a GP-LPS alone vaccine provided. This is the first report of a protein supplementing protection induced by LPS in a Francisella vaccine. This paves the way for developing an effective, safe subunit vaccine for the prevention of inhalational tularemia, and validates the GP platform for vaccine delivery where complex immune responses are required for prevention of infections by intracellular pathogens.

Transplantation of cultured thymic fragments: results in nude mice. V. Reconstitution with xenogeneic (rat) thymic tissue

Transplantation of F344 rat cultured thymic fragments was able to restore immune function to nude mice. Approximately half of such animals displayed increased lifespan (7-8 months). These mice were also capable of rejecting allogeneic mouse skin and rat skin from a strain (Buffalo) unrelated to the thymus donor; however, they were incapable of rejecting rat skin from the thymus donor strain. Proliferative responses to T-cell mitogens were restored. Proliferative responses to alloantigens and xenoantigens in mixed leucocyte cultures were also restored and showed the same patterns of specific reactivity and non-reactivity as in skin graft rejection. The ability to make antibody responses to specific antigens was also restored, but the responsiveness was more variable than for cell-mediated responses. Some mice were able to make antibody to rabbit serum proteins; however, fewer mice made antibody to ovalbumin. The inability to respond to ovalbumin may be due to the fact that F344 rats are low responders to this protein. These results suggest that cultured xenogeneic thymus is effective in restoring two major differentiation functions of the normal thymus gland: development of specific antigen responsiveness and non-responsiveness.

Carrageenan-induced suppression of T-lymphocyte proliferation in the rat: abrogation of suppressor factor production by the prostaglandin synthesis inhibitors, indomethacin and ETYA

Carrageenan, an algal polygalactan reputed to be selectively toxic for macrophages, is widely employed as a tool to dissect pathways of cell-mediated immunity. In the present study, corn oil-elicited rat peritoneal macrophages after 72 h culture with 10 micrograms/ml Seakem 9 Carrageenan secreted a soluble suppressor factor capable of abrogating T-cell activation by phytohemagglutinin-P (PHA). Addition of the prostaglandin synthesis inhibitors Indomethacin or 5,8,11,14-eicosatetraynoic acid (ETYA) prevented inhibitor synthesis by Carrageenan-conditioned macrophages. Seakem 9 and lambda Carrageenans added directly into spleen cell cultures failed to diminish lymphocyte proliferation, but rather stimulated spleen cell division. Macrophages cultured with low concentrations of Carrageenan appeared to be activated on the basis of enhanced tumoristatic capacity against Schmidt-Ruppin sarcoma cells. Thus, macrophages activated by low concentrations of Carrageenan in vitro appear to secrete a product of arachidonic acid metabolism which is a potent inhibitor of PHA-induced spleen cell mitogenesis.

Genetic control of neutralizing antibody response to mouse interferon in rats

Various strains of rats were immunized weekly with mouse interferon (IFN containing both IFN-alpha and IFN-beta). Their sera were examined for the ability to neutralize the antiviral activity of IFN in a microtiter assay. DA and ACI (RT-1a), BN (RT-1n), and WF (RT-1w) strains of rats produced anti-IFN antibodies after a minimum of four inoculations. In contrast, neither Lewis (RT-1l) nor Buffalo (RT-1b) strains of rats produced any detectable anti-IFN antibodies even after 12 weekly inoculations of IFN. This lack of responsiveness could not be overcome by immunization in the presence of Freund's complete adjuvant. The genetic basis of this difference in antibody response was examined using F1 and back-cross generations of rats. Both (ACI X LEW) F1 and (LEW X ACI) F1 rats produced titers of anti-IFN antibody intermediate to the parental strains. No maternal or paternal effects were observed. Results from the back-cross generation of F1 rats to the parental strains suggested that although the major histocompatibility complex may be a factor in control of this response, other genes are also involved.

A comparison of the immune response between two lines of chickens selected for differences in the weight of the bursa of Fabricius

Experiments were designed to compare antibody-mediated immunity in two lines of 5-month-old chickens previously selected for a large or small bursa. After receiving a primary or secondary challenge with sheep-red-blood cells, bovine serum albumin, or dinitrophenyl, birds from the small bursa line (SBL) were significantly more efficient antibody producers than birds from the large bursa line (LBL). However, Immunoglobulin G synthesis by SBL birds was significantly lower than in LBL birds.

Murine respiratory mycoplasmosis in F344 and LEW rats: evolution of lesions and lung lymphoid cell populations

By comparison of two strains, LEW and F344, which are known to differ in susceptibility to Mycoplasma pulmonis respiratory disease, it was shown that differences in lesion severity and progression were associated with changes in lung lymphocyte populations. Lung lesions in LEW rats developed earlier after infection, became more severe, and were characterized by continued proliferation of all classes of lymphoid cells, T lymphocytes, B lymphocytes, and plasma cells, throughout the 120-day observation period. In contrast, lymphoid proliferation in F344 rats reached a plateau at 28 days and was restricted to an increase in T lymphocytes, immunoglobulin A (IgA)-bearing B lymphocytes, and IgA and IgG plasma cells. Although approximately 10 times as many IgG B cells and 4 times as many IgG plasma cells were found in infected LEW rats as compared with F344 rats, the specific anti-M. pulmonis IgG response in the two strains was roughly parallel. The same relationships held true, although to a lesser extent, for specific IgA antibody responses and cellular responses. Whereas lung lesions showed a tendency to resolve in F344 rats by 120 days, severe lesions persisted in LEW rats. The disparity between the cellular response and specific antibody response, the seemingly uncontrolled lymphocyte proliferation in LEW rats, and the mitogenic potential of M. pulmonis suggest that differences between LEW and F344 rats in lung lesion severity and progression are related to differences in the degree of nonspecific lymphocyte activation in the two strains, an imbalance in regulation of lymphocyte proliferation in LEW rats, or both.

Investigations on the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on parameters of various immune functions

The effects of TCDD exposure on parameters of immune function during the developmental period were investigated. Exposures were performed in Fischer/Wistar rats. Fetal and neonatal rats were exposed to TCDD through maternal dosing (5 micrograms/Kg) on day 18 of gestation and on days 0, 7, and 14 of postnatal life (group 1). Another group of neonatal rats were exposed to TCDD through maternal dosing on days 0, 7, and 14 of postnatal life only (group 2). Body weights and relative thymus weights were found to be suppressed up to 135 days of age in group 1 but only up to 35 days of age in group 2. Parameters of cell-mediated and humoral immune function were investigated. TCDD suppressed cell-mediated immune function without affecting humoral immune function. TCDD-exposed animals had recovered normal cell-mediated immune function by 270 days of age. A group of inbred Fischer rats was exposed to TCDD as described for group 1 above. At 45 days of age these animals were utilized in lymphocyte homing studies. It was found that TCDD exposure alters homing patterns of lymphocytes from exposed animals when adoptively transferred to untreated animals. In addition, lymphocytes from nonexposed animals did not home normally when injected into TCDD-exposed recipients.

Genetic control of the immune response to mammalian chymotrypsins in mice. I. The immune response to high doses of bovine alpha-chymotrypsin

The primary and secondary immune response to the antigen bovine pancreatic alpha-chymotrypsin was investigated in inbred mice. It was found that strain differences in the immune response only became apparent after secondary immunization. The genetic control of the immune response was investigated in twelve different strains of mice, F1, F2 and F1 backcross hybrids, following secondary immunization. A continuous distribution for the mean antibody responsiveness was obtained. High responsiveness was associated with both the H-2 haplotype and three non-H-2 loci. Furthermore the F1 hybrids produced a greater quantitative antibody response to chymotrypsin than either of the corresponding parental strains.

Strong and weak immune responses across the same major histocompatibility barrier in rats

Inbred rat strains, Fischer 344 (F-344) and Lewis (LEW), share the serologicalAg-Bl allele and react very weakly in mixed lymphocyte culture (MLC). Despite this apparent identity atAg-B, these strains differ markedly in their immune responses to anAg-B disparate third strain Marshall 520 (M-520) (Ag-B6). F-344 recipients allowed M-520 heart grafts an extended survival, whereas LEW recipients rejected them rapidly. F-344 and M-520 showed a weak response in MLC in contrast to a strong response for LEW and M-520. F-344 produced antisera in response to injection of M-520 cells that had a relatively high antibody titer but low cytotoxic activity. F-344 responded to another strain, Buffalo (BUF) (alsoAg-B6), in a similar fashion. F-344 apparently can produce a strong allogeneic response, as it was able to rapidly reject heart grafts from (LEW x Brown-Norway) F(1) donors (LBN) (Ag-B 1/3). The low response of F-344 to M-520 probably was not due to shared antigens between the two strains because M-520 heart grafts underwent rapid rejection in LEW hosts highly tolerant to F-344. To explain the contrasting response of F-344 and LEW to theAg-B6 disparity, we propose that it is controlled by an immune-response gene(s); that F-344 has a low-responding allele and LEW has a high-responding allele. The data do not reveal a location for this proposed gene. The high-responding allele appears to be dominant, as M-520 hearts were rejected rapidly by (F-344 x LEW) F(1) recipients.

Immune response gene (Ir-SRBC) exerts its effect via macrophages in inbred rats

In the previous report, strain differences of inbred rats were investigated in the antibody response to sheep erythrocytes (SRBC). A low-responder strain (Fischer rats) produced only IgM antibody, but other high-responder strains switched over from IgM to IgG antibody to SRBC. Pretreatment with incomplete Freund's adjuvant made Fischer rats a high-responder. These results seemed to indicate that there are malfunctions of macrophages, together with T cells, in Fischer rat strain. In this report, strain differences in the phagocytic activity of macrophages were examined using radiolabelled SRBC. High uptake of SRBC by the spleen in the low responder rats, and vice versa, was confirmed in various experimental conditions. Genetic analyses were made of the specific spleen uptake of the radiolabelled SRBC in backcrossed rats. The result clearly showed that the degree of spleen uptake of the radiolabelled SRBC is genetically determined by a single gene and this property itself has a close negative correlation with the ability of each rat to produce haemolysin against SRBC. These results strongly suggest that the Ir-SRBC gene exerts its effect, at least in part, via macrophages. The relationship between the function of the macrophage and the antibody response is discussed.