Single-step immunosorbent preparation of F-protein from mouse liver with conservation of the allo-antigenic site, and determination of concentration in liver and serum

A single-step immunopurification procedure is described for murine protein F, in which the T-cell-defined allo-antigenic site on the protein is fully conserved. The procedure is based on the use of a newly developed monoclonal antibody. The protein is isolated as a 42,500 mol. wt (F.1) and a 43,000 mol. wt (F.2) monomer. The content in liver, as estimated by radioimmune inhibition assay, is 0.083% and the yield is approximately one third. An assay of immunogenic activity in adoptive transfer, which detects the T-cell-defined site, provides a similar estimate of content in liver. The adoptive transfer assay yields concns of F-protein in serum of young mice of 0.5-1.2 X 10(-9)M, the lowest concn of protein known to induce complete immunological tolerance.

An appraisal of survival strategies

Only a few years ago parasite immunology looked an unattractive subject better left to the dogged specialists. Parasites and hosts had been playing chess together for a million years, and there seemed little prospect of perturbing matters in favour of the host immune system. All that has changed, for three reasons. Firstly, we have learned how to grow at least some parasites in vitro, and prospects of doing so with others are encouraging. Secondly, progress in cellular immunology has revealed the sort of loopholes in the host defence system which parasites are likely to exploit: we are learning the questions which matter about parasites as antigens. Thirdly, and most importantly, molecular genetics is being brought to bear on parasites: we can now see a real, though long-term, prospect of manufacturing practicable vaccines through bio-engineering, and more immediately it gives us the tools needed to probe the host immune responses in the form of cloned antigens.

Self- and allo-specific suppressor T cells evoked by intravenous injection of F protein

The liver/serum protein F appears to inactivate clones reactive towards itself in the T helper cell but not the B cell compartment. To examine the extent of self-reactivity in the T suppressor cell compartment, the well-established procedure of i.v. injecting milligram doses of the protein was used. To detect suppression, an entirely in vitro proliferation assay was devised, based on use of immunopurified F antigen. In this way T suppressor cells could be detected after activation either by allogeneic F, or (though to a lesser extent) by self-F protein. Thus the T suppressor cell compartment contains potentially self-reactive clones, and to that extent the receptor repertoire of T suppressor cells overlaps with B rather than T helper cells.

Allospecific suppression without requirement for participation of Ly 2+ cells

Haplotype-specific suppressor T cells (Ts) were induced by incubation of mouse spleen/lymph node cells with allogeneic heat-treated cells. These Ts have an Ly 1+2- phenotype, and can be activated in cultures depleted of Ly 2+ cells by treatment with anti-Ly 2 antibodies and complement. In addition, these Ts inhibit alloantigen-induced proliferation of Ly 1+2- cells without the participation of Ly 2+ cells. These results show that allospecific suppressor T cells can be activated and can act without participation of Ly 2+, thus demonstrating that Ly 1+2- cells can directly suppress proliferation of other Ly 1+2- cells.

Helper T cell activity demonstrated by thymic nurse T cells (TNC-T)

Culture supernatants of mixed lymphocyte reactions (MLR) between AKR thymic nurse T cells (TNC-T) as responders and irradiated DBA/2 spleen cells as stimulators, induce significant proliferation of concanavalin A (Con A)-stimulated DBA/2 thymocytes. The culture supernatants of MLRs using extra-TNC thymocytes (ET) as responders do not show this activity, and the addition of thymus epithelium did not enable a response to take place. Again, unlike ET, TNC-T cells could also give a positive allogeneic response. Irradiated AKR TNC-T cells stimulated allogeneic BALB/c spleen B cells to produce immunoglobulin. These observations indicate that cells in the TNC-T pool are more mature than those in the ET pool.

Antigen-presenting cells do not discriminate between self and nonself

The immune response to F protein in mice provides a system in which the capacity of antigen-presenting cells to present autologous protein to T cells can be examined. When we used the F-type 1 (F.1) and F-type 2 (F.2) combination, these cells proved equally able to present autologous and foreign protein in both an in vivo adoptive transfer and an in vitro proliferation assay. This formally excludes the possibility that these cells themselves discriminate between self and nonself, while still allowing the possibility that their uptake of antigen may be regulated by lymphocyte products.

Thymic epithelial cells derived from the cultures of thymic nurse cells

Thymic epithelial cells are derived from the cultures of thymic nurse cells. These cultures are free from fibroblasts and macrophages. The epithelial nature of these cells is confirmed by demonstrating the presence of keratin filaments in them. These epithelial cells show heterogeneity in shape, size and distribution of keratin filaments. They contain nonspecific esterase(s) molecules and express both I-A and H-2K antigens.

Haplotype-specific suppressor T cells mediating linked suppression of immune responses elicited by third-party H-2 alloantigens

Specific suppressor T cells (Ts) were induced in vitro by incubation of mouse spleen/lymph node cells with allogeneic heat-treated cells. These Ts inhibit mixed lymphocyte reaction (MLR) in a haplotype-specific manner. Ts also suppress cell proliferation induced by third-party H-2 alloantigens provided these are expressed on the same cell surface as at least some of the H-2 antigens used for Ts activation. Ts activated by H-2 plus non-H-2 alloantigens suppress an MLR induced by irrelevant H-2 alloantigens if these are expressed on the same cell surface as the non-H-2 alloantigens used for Ts activation. Products of the H-2 region or non-H-2 alloantigens which are not able to stimulate cell proliferation do not activate Ts. These Ts are first demonstrable after 4 days of incubation of lymphoid cells with heat-treated allogeneic cells and they inhibit MLR only if added at the very beginning of the culture. Exogenous interleukin 2 does not overcome suppression and the suppression is not due to a cytotoxic effect, since heat-treated cells do not elicit cell proliferation or cytotoxic cells. Moreover, the specific Ts differ in their Thy-1+,Ly-1+,2-phenotype from Ly-2+ allospecific cytotoxic cells. Thus specific Ts could be induced in vitro, which demonstrate linked suppression for third-party H-2 alloantigens provided these are expressed on the same cell surface as the antigens used for Ts activation.

Does clonal selection occur among T cells?

Several lines of evidence indicate that T cells proliferate in response to antigenic stimulation to only a very limited extent, and certainly markedly less than do B cells. We here summarize new evidence showing (1) that even under conditions of in vivo immunization, T cells rapidly reach a plateau of activity which does not rise even upon repeated stimulation, and (2) that the plateau is reached so rapidly that the initial frequency of responding cells must be high. Our evidence for these conclusions comes from studies on adoptive immunization in which the activity of T cells activated in vivo and cell lines selected in vitro are compared.

T-cell responses to minor histocompatibility antigens

We have investigated the helper and cytotoxic T-cell response to minor histocompatibility antigens and generated long term antigen-specific cell lines to them. Antigen-specific activity was selected for by regular restimulation with irradiated cells bearing the antigens in the presence of interleukin 2, so that alloreactivity to other cell surface antigens was gradually lost. Helper T cells cultured over several months were active in vivo and in vitro, but the culturing method eventually selected for cytotoxic T cells at the expense of helper T cells, with concomitant changes in the proportions of cells expressing the Lyt phenotypes. Individual long term cultures of cytotoxic T cells specific for minor histocompatibility antigens were restricted by either H2K or D but not both. Helper T cells to minor histocompatibility antigens derived directly from primed F1 mice did not show restriction to the priming parental haplotype. This is consistent with antigen reprocessing by the F1 antigen presenting cells such that populations of helper T cells restricted by both parental H-2 haplotypes were primed. F1 cytotoxic T cells were restricted to the parental H-2 haplotype used for in vitro boosting, irrespective of which H-2 was used for in vivo priming.

Allospecific T-cell lines with functional activities

A T-lymphocyte line and sublines from it reactive with Class II MHC alloantigens have been examined for proliferative responses and helper activity in vitro and in vivo. Both the parent cell line and its derived sublines recognize alloantigenic determinants encoded for by the I-A subregion of the H-2 complex in a proliferative assay, and have regulatory activity for allogeneic and syngeneic B cells in two different helper systems. The in vitro selected cell populations are approximately twenty-fold more active in functional helper assays than populations selected in vivo by priming. Differential analysis of the patterns of proliferative responses of sublines against allogeneic I-A molecules on different backgrounds indicates that one type of selected cells reacts preferentially to MHC molecules presented on the background used for selection.

An adoptive cell transfer system for the evaluation of immunity to Herpes simplex virus in mice

Lymphocytes adoptively transferred from syngeneic immune donors protect mice against challenge with Herpes simplex virus type 1. Normal mice require transfer 3 x 10(7) spleen cells for protection. Sublethal irradiation (450 rad) decreases the number required five-fold. Lymphocytes from non-immune donors do not protect, and hyperimmunization does not enhance the protection efficiency of donors. The viral LD50 varies through a range 10(5)-fold during the period of recovery from this amount of radiation, but over the same period there is little variation in the number of cells required for protection. Nor is there much variation in this number between strains of mice naturally susceptible (CBA) and resistant (C57) to the virus. We conclude that natural resistance operates at a level of virus handling prior to operation of the lymphocyte system, perhaps at the generation of interferon. As few as 1.3 x 10(6) immune T lymphocytes can protect against challenge provided that they are transferred together with normal spleen cells. We conclude that primed lymphocytes act in co-operation with non-immune cells.