Symposium on in vitro studies of the immune response. IV. Role of nucleic acids in the anamnestic antibody response

A kinetic and quantitative analysis of antibody and protein synthesis during the primary response to keyhole limpet haemocyanin

Rabbits were injected with alum-precipitated keyhole limpet haemocyanin. On various days after immunization popliteal lymph node cells were prepared for synthesis of antibody as well as non-antibody proteins by incorporation of ¹⁴C-amino acids. Antibody and proteins were characterized by gel filtration, radio-immunoelectrophoretic and zone electrophoretic analyses of the culture media. Some `natural' antibody appeared to be synthesized by lymph node cells from uninjected animals. The first definite increase in numbers of nucleated lymph node cells and in antibody synthesis occurred on the third day after immunization. The peak of cell numbers and antibody synthesis was attained on the sixth day after antigenic stimulation. The antigen-stimulated cells also synthesized increased amounts of non-antibody proteins, including IgM and IgG, and proteins tentatively identified as α₂ macroglobulin, α₁ globulin and a microglobulin. Most of the radioactive protein which was synthesized following injection of antigen was demonstrably not antibody. Both IgM and IgG antibody were synthesized at all times, but relatively more radioactivity was incorporated into IgM antibody on day 3 and into IgG antibody on day 6 after immunization.

Regulation of the secondary antibody response in vitro. Enhancement by actinomycin D and inhibition by a macromolecular product of stimulated lymph node cultures

Two opposite effects of actinomycin D on antibody synthesis have been studied in organ cultures of rabbit lymph node fragments. These cultures were prepared from previously primed rabbits and stimulated with antigen(s) on day 0 to yield a secondary response, whose inductive phase extended to about day 9 and whose productive phase may last for several months in the serum-free medium described here. Concentrations of actinomycin D above 0.01 microM (0.012 microg/ml) produce inhibition of antibody synthesis during both phases of the response. However, antibody synthesis is about 10 times more sensitive to inhibition by this drug when it is added during the inductive phase than during the productive phase. During the latter phase, synthesis is more rapidly terminated as the drug level approaches 10 /microM (12.5 microg/ml). At this level the 50% synthesis time is about 2.8 hr, which is identical with that found when 5-10 microM puromycin is added to the medium of parallel cultures. Transient enhancement of antibody synthesis is frequently produced by a brief exposure to low levels of actinomycin D (generally less than 0.01 microM). Enhancement appears in precise temporal association with actinomycin pulses added for 2 days or less only between days 6 and 16. This apparent enhancement of antibody synthesis resembles the increased enzyme synthesis described by Garren et al. (6) and led to a search for an antibody-inhibitory material (AIM) whose synthesis might be stopped preferentially by low levels of the drug. Stimulated lymph node cultures produce between days 6 and 15 a nondialyzable material which inhibits antibody synthesis during the productive phase of heterologous antigen-antibody culture systems. Just as enhancement with low levels of actinomycin D appears within 2 hr after the drug has been added to cultures, so inhibition occurs within 4 hr of adding AIM to cultures during their productive phase. These observations suggest that AIM is analogous to the translational "repressor" postulated by Garren et al. (6). AIM has relevance in two areas of immunology: (a) it may be the explanation for many examples of antigenic competition, and (b) it may represent a normal control mechanism for the productive phase.

Haemolytic plaque formation by mouse peritoneal cells, and the effect on it of Friend virus infection

Peritoneal cells from non-immunized mice, when incubated in vitro with sheep red cells and complement in a film of carboxymethyl-cellulose gum, form plaques of haemolysis after a latent phase of 15–20 hours. Plaques are also produced by the free cells of the pleural cavity but not by lymph node, spleen, thymus and bone marrow cells. Plaques are not produced at room temperature, nor when the complement has been inactivated or the peritoneal cells have been heat-killed. The phenomenon is age-dependent: the peritoneal cells reach the highest activity when the donor mice are about 10 weeks old.

By testing purified populations of lymphocytes and macrophages the cell type responsible for plaque production has been identified as the lymphocyte.

Plaque formation is suppressed in the presence of an anti-mouse immunoglobulin serum without any detectable effect on cell viability or anticomplementary action. This suppressive effect is destroyed by prior precipitation of the antiserum with normal mouse serum.

A technique which facilitates the study of peritoneal cells from individual mice has been developed and applied to peritoneal cells from Friend virus-infected mice. The activity of peritoneal cells 10 days after intravenous or intraperitoneal infection is similar to that of their uninfected counterparts. Peritoneal cells from mice killed 17 days after intravenous infection or 19 days after intraperitoneal infection form significantly reduced numbers of plaques. The reduced activity is accompanied by a decrease in the percentage of lymphocytes present in the peritoneal population of the infected mice.

High-dose delay of the immune response. Effect of actinomycin D on continuation of the immune response in vitro

The continuation of the primary and secondary antibody response to human serum albumin (HSA), induced in vivo, was followed in explanted chicken spleen fragments. The effect of actinomycin D (AMD) on the in vitro response was studied in spleens from chickens injected with various doses of HSA and removed at differing intervals after injection. The antibody response of "early spleen" cultures was AMD-sensitive, while cultures of spleens removed later were AMD-resistant. It was suggested that this shift represented the development of cells with in vivo preformed RNA involved in specific immunoglobulin synthesis. With increasing doses of HSA, the AMD-sensitive phase was prolonged, suggesting the delay of mRNA formation or some other AMD-inhibitable process in vivo. With large doses of HSA, the immune response in vitro was decreased, starting after a 1-2 day delay and not occurring in the presence of AMD. Massive doses of HSA completely inhibited the continuation of the response in vitro by spleen fragments removed between the 2nd and 5th day after injection. The results point to the controlling role of antigen dose in determining the onset of macromolecular synthesis during immunocyte maturation.

Expermental salmonellosis. XI. Induction of cellular immunity and formation of antibody by transfer agent of mouse mononuclear phagocytes

When mice were injected intraperitoneally with a ribonucleic acid (RNA) preparation extracted from the peritoneal mononuclear phagocytes (termed monocytes) of immunized mice, these macrophages developed cellular immunity and cellular antibodies. The peritoneal monocytes were obtained from normal mice and maintained in tissue culture bottles in a homogeneous cell population. When they were treated in vitro with an immune RNA preparation, they acquired cellular immunity, and cellular antibodies were detectable in such monocytes. These results suggest that the mononuclear phagocytic cell line constitutes a cell line responsible for antibody formation.

Synthesis of gamma G antibody and immunoglobulin on polyribosomes in a cell-free system

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Primary antibody response in vitro in peritoneal cells

Peritoneal cells (PC), from nonimmunized mice, incubated in a carboxymethyl cellulose gum containing sheep red blood cells (SRBC) and guinea pig complement (following the technique of Ingraham and Bussard) start to produce plaques of hemolysis 20 hr after the beginning of incubation at 37 degrees C. In contrast, spleen cells from immunized mice complete their plaque-forming activity in 6 hr. The fact that formation of plaques by previously uncommitted cells is related to the life of the leukocytes, and is complement dependent brings evidence that we are dealing with an immunological phenomenon. Puromycin suppresses the formation of plaque. Previous incubation of the PC with SRBC in liquid medium, before incorporation in the detection system, reduces the lag in the production of plaques. This indicates that a phase of stimulation precedes the phase of expression (manifested by plaque formation). The immunological activity of the peritoneal cell suspension is highly dependent on the concentration of the suspension, which indicates that this activity results from a cooperative process. Actinomycin D, which does not suppress the production of plaques by cells from immunized animals, stops completely the in vitro induction. It is concluded that we have probably observed a primary immune response induced in vitro.