Primary antibody response in vitro in peritoneal cells

Translating molecular insights in autoimmunity into effective therapy

Autoimmunity and the pathogenesis of autoimmune diseases were a major focus of the Walter and Eliza Hall Institute, where I started my research career. After my initial studies on immune cell culture and immune regulation, I returned to an analysis of the pathogenesis of human autoimmunity in London. Linking upregulated antigen presentation to autoimmunity led to an investigation of the role of cytokines in rheumatoid arthritis (RA), in collaboration with Ravinder Maini. These experiments defined the concept of a TNF-dependent cytokine cascade driving the manifestations of RA, which led to successful clinical trials of anti-TNF monoclonal antibody in RA patients, heralding a major change in medical practice. This success was made possible by enthusiastic support from many laboratory and clinical colleagues and taught us that cytokines are important rate-limiting steps and hence good therapeutic targets. My current scientific challenge is exploring the hypothesis of whether all major medical needs can be approached via cytokine blockade.

Antibody forming cell precursors among glass-adherent peritoneal exudate cells

Among glass-adherent peritoneal exudate cells (gaPEC), induced by an inoculation of 1% glycogen solution, about 4.5% were classified as antibody-forming cell precursors (AFCP) on the first day of culture by means of anti-mouse B-cell antibody (anti-B-Ab). They proliferated and differentiated into IgG-forming plasma cells when cultured with antigen and thymic RNA in vitro. Pretreatment of PEC with anti-B-Ab and complement suppressed the formation of plasma cells. AFCP had receptors for IgM-antigen complexes and for complement, both of which were independent of Ca++ and MG++ and resistant to treatment by pronase or phospholipase C. Cells bearing detectable receptors for EA (IgM) an EAC diminished by the 6th day when gaPEC were cultured with thymic RNA, but persisted longer in cultures without thymic RNA. The same percentages of cells demonstrated tartrate-resistant acid phosphatase activities but were devoid of esterase. Twenty to thirty percent of anti-B-Ab sensitive cells ingested latex particles. The proliferation kinetics of IgG-forming cells were studied through the 21st day of culture by means of peroxidase-labeled antibody staining methods.

Immunodepression by Rowson-Parr virus in mice. II. Effect of Rowson-Parr virus infection on the antibody response to sheep red cells in vivo and in vitro

The effects of infection with Rowson-Parr virus (RPV), an associated virus present in Friend virus (FV) preparations, on the splenic plaque-forming cell response to sheep red cells in adult mice and on the plaque-forming cell response of peritoneal cells in vitro have been investigated. The results support the hypothesis that RPV might be responsible for a considerable proportion of the early immunodepressive effects caused by FV preparations.

Functional symmetry amongst daughter cells arising in vitro from single antibody-forming cells

The open carboxymethylcellulose (CMC) haemolytic plaque technique was used to study the antibody-forming capacity of daughter cells arising from single plaque-forming cells (PFC) after in vitro mitosis. Spleen cells from mice immunized 2–5 days previously with sheep red blood cells (SRBC) were used. The number of in vitro mitoses was increased by giving mice colcemid 2 hours before killing. The experimental protocol involved allowing cells to form haemolytic plaques in a liquid medium; selecting the largest available PFC; transferring them to wash droplets to await colcemid-escape and completion of mitosis; separating the two daughter cells from each other by micromanipulation; transfer of each daughter cell pair to a CMC plaque-revealing monolayer; and continuous assessment of plaque formation rate by daughter cell pair members. The whole procedure was carried out with the micromanipulation set up at 37°. Altogether, seventeen experiments on IgM (direct)-PFC and two on IgG (enhanced)-PFC were performed.

Of eighty-seven daughter cell pairs transferred, eighty-six behaved symmetrically with both daughter cells forming antibody (seventy-four cases) or not forming antibody (twelve cases). Arguments are presented to suggest that this failure rate of 14 per cent is due to technical factors inherent in the micromanipulation steps. In the great majority of cases, daughter cells were symmetrical in size and plaque formation rate. Plaques from daughter cells were always of similar morphology, and when mixed sheep and goat RBC monolayers were used to reveal plaques, both cells of a pair always behaved similarly in that either both formed a clear plaque or both formed a turbid plaque.

The results are discussed in the light of the hypothesis of Tannenberg and Malaviya (1968) for asymmetric divisions amongst PFC, which they do not favour. It is stressed, however, that the possibility of asymmetric divisions amongst antibody-forming cell precursors is not eliminated.

Characterization of the antibody response to type 3 pneumococcal polysaccharide at the cellular level. I. Dose-response studies and the effect of prior immunization on the magnitude of the antibody response

The cytokinetics of the antibody to Type III pneumococcal polysaccharide (SSS-III) were characterized by an immuno-plaque procedure using erythrocytes sensitized with SSS-III. Prior immunization, irrespective of the doses employed, did not result in the development of immunological memory; instead, low-dose paralysis was produced in mice previously immunized with all doses of SSS-III.

Dose-response studies revealed that within a given dose range, there was a direct relationship between the immunizing dose and the magnitude of the antibody response obtained. The dose-response curve for SSS-III showed a single optimal dose for immunization; doses only slightly in excess of the optimal dose produced a significant reduction in the magnitude of the antibody response. The implications of these findings, with respect to the development of paralysis to SSS-III, are discussed.

The effects of RES 'blockade' on antibody formation. IV. Inhibition of plaque-forming cells in spleen cultures treated with carbon particles

The effects of colloidal carbon particles on induction of antibody-forming cells in tissue-culture suspensions of spleen cells from normal or sheep erythrocyte primed donor mice were determined. Addition of carbon to normal spleen-cell cultures prevented induction of the `primary' type immune response in vitro. The time at which the carbon was added to the cultures was important, since less suppression occurred when carbon treatment was delayed 48 hours after initiation of culture. Furthermore, the most suppression occurred with the largest dose of carbon used.

Injection of normal donor mice with carbon at various time intervals prior to death interfered with the ability of the spleen-cell suspensions to respond to sheep erythrocytes in vitro by formation of antibody plaques. Maximum suppression occurred when the donor mice were treated with carbon 1–2 days before they were killed.

The anamnestic antibody plaque response in vitro was also suppressed by addition of carbon particles to spleen-cell cultures derived from mice primed with sheep erythrocytes several weeks before they were killed. There was a greater suppression of the 7S than 19S PFC response in vitro. However, the only marked suppression occurred when the highest dose of carbon was used and when it was added to the cultures at `0' time.

Direct injection of carbon into mice primed with sheep erythrocytes 3–4 weeks previously also interfered with the secondary response of the spleen-cell cultures in vitro. Both 19S and 7S antibody-forming cells were suppressed, with a greater suppression of 7S PFCs.

The results of these experiments were interpreted as indicating that phagocytic cells, capable of being `blockaded' in vitro or in vivo by carbon suspensions, are necessary for induction of both primary and secondary type antibody plaque responses in vitro. It seems likely that the carbon particles compete with the red blood cell antigens for a limited number of antigen-processing cells.

In vitro stimulation of antibody formation by peritoneal cells. 3. Effect of active immunization on the subsequent in vitro performance of peritoneal and spleen cells

Male CBA mice were given a single intraperitoneal injection of sheep red blood cells (SRBC) or horse red blood cells (HRBC). They were killed at intervals of 1–10 days thereafter, and micro-cultures of spleen cells or peritoneal cells (PC) were prepared. These consisted of a thin film of tissue culture medium containing carboxymethyl cellulose (CMC), mouse lymphoid cells, guinea-pig complement and either SRBC or HRBC, held at 37° under liquid paraffin. Cultures were read repeatedly for appearance of haemolytic plaques.

PC from SRBC-immunized mice showed an altered reactivity on SRBC monolayer cultures. The peak plaque count achieved in vitro fell progressively for 4 days after immunization, and then returned to normal by day 7. The actinomycin D resistant component of the PC response rose rapidly; at 1 day after immunization it was equal to the total response. Over the next 3 days after immunization it fell again to normal levels. The results suggested that the in vivo injection sets in train events locally in the peritoneal cavity which resembled those following in vitro culture of normal PC in SRBC monolayers. The effects were immunologically specific as only marginal changes followed the injection of HRBC.

Spleen cells from SRBC-immunized mice, when cultured in SRBC monolayers, yielded many cells capable of giving plaques after 5–60 minutes incubation, as expected. These were deemed to be cells forming antibody at the moment of killing of the animal. In addition, such cultures developed new plaques over the subsequent 23 hours in culture. These were produced by cells not initially forming antibody which switched into antibody secretion at some time during culture. At early time points after immunization, this second type of cell was much more numerous than the first type. The switch from non-secretor status could occur in the presence of a high concentration of actinomycin D. Operationally these non-secretors in immunized spleens resembled an important fraction of PC from unimmunized retired breeder mice. The progressive conversion of non-secretor cells into secretors, if it occurs in vivo, would have a major influence on the kinetics of appearance of PFC in a spleen after immunization.

While spleen cells from mice immunized with HRBC performed on HRBC monolayers much as described above, PC from HRBC-immunized mice could not be induced to cause significant lysis in HRBC monolayers. The same was true of PC from mice chronically fed with HRBC. In fact, no method has yet been found to persuade PC to produce lytic plaques active against erythrocytes other than SRBC.

Quantitation of strain BALB-c mouse peritoneal cells

Total and differential counts of the peritoneal cells of male and female BALB/c mice aged 10 days to over 2 years demonstrate that the increase in cell number that occurs in mice over 2 months old is due entirely to an increase in lymphocytes. The number of peritoneal macrophages in BALB/c females is maintained at a constant level for 22 months. The stability of the macrophage population in contrast to the increase in numbers of lymphocytes suggests that the body pools of these two cell types are not related.

Maturation of hemolysin-producing cell clones. II. The appearance and localization of precursor units in lymphoid tissues of neonatal mice

Cells capable of reacting with sheep erythrocyte (SRBC) antigen to maturate and produce hemolysin appear simultaneously in the bone marrow and spleen of 1-day old Swiss-Webster mice. However, hemolysin-producing cell clones (HPCC) do not result. Complete functional precursor units generally appear in the spleens of mice older than 3 days. In vivo and in vitro data correlate well in this regard. Complete precursor units are not seen in the bone marrow and only very rarely in the thymus. The efficiency of precursor units of neonatal mice when they become functional approximates that of the mature animal when based on the doubling time of plaque-forming cells (PFC). Possible explanations of the initial appearance of incomplete precursor units have been discussed.

Peyer's patches: immunologic studies

The immune capabilities of the Peyer's patches have been investigated by the use of an in vitro system. Despite our failure to stimulate Peyer's patch lymphocytes in vivo it appears that Peyer's patches behave immunologically as peripheral lymphoid tissues. Cultures prepared from the dissociated Peyer's patches of normal rabbits respond to sheep erythrocytes. The response is comparable to that obtained with spleen cultures from the same animals and is not dependent on the presence of the epithelial cells which line the lumen. Similar thymic cultures do not respond. Our experiments with cultures prepared from rabbits which have received one or two injections of SRC show that the Peyer's patches contain both IgM and IgG "memory" cells which have migrated from the spleen. The concentration of these cells in the spleen remains several hundredfold higher.

In vitro stimulation of antibody formation by peritoneal cells. II. Cell interactions and effects of immunochemical or metabolic inhibitors

Peritoneal cells (PC) from normal, unimmunized mice were placed in ultra-thin monolayer cultures containing carboxymethylcellulose (CMC), sheep red blood cells (SRBC), and complement, and tested for the appearance of plaques of lysis. The behavior of PC from young male mice and from female mice that had given birth to several litters (retired breeder mice) was studied. It was found that cells from spleen, mesenteric lymph node, thymus, bone marrow, thoracic duct lymph, or Peyer's patches could not form plaques in the CMC microcultures. Also, various combinations of these cells did not lead to plaque formation. When cells from any of these sources were mixed with PC, there was either no effect or an actual inhibition of plaque formation, the plaque counts being lower than would have been expected from the number of PC present in the mixture. Optimal plaque formation by peritoneal cells was found to be dependent on an optimal cell concentration, this optimum being around 5 x 10(6)/ml for young male mice and 0.5 x 10(6)/ml for retired breeders. Inhibition of plaque formation was found with either supra- or suboptimal cell concentrations. The inhibition by excess cell concentration may have been a simple nutritional or nonspecific overcrowding effect, as it could also be induced by an addition of an excess of spleen or lymph node cells. The failure of more dilute PC preparations to give adequate numbers of plaques appeared to be more specific, as plaque numbers could not be restored to normal by addition of spleen cells. The suggestion was that some cell to cell interaction between PC was involved. This dependence on cell concentration was not seen with immunized spleen PFC. Plaque appearance could be specifically and reversibly suppressed by placing PC in a medium containing rabbit anti-mouse IgM serum. Anti-IgG serum had no such effect. These experiments strengthened our view, expressed in the accompanying paper, that plaque formation was due to the formation of IgM, hemolytic antibody to SRBC by the PC. Metabolic inhibitors were incorporated into monolayer cultures and had different effects with the different types of PFC used. In the case of spleen cells from mice actively immunized against SRBC 4 days before killing, actinomycin D had no effect on plaque counts and puromycin reduced plaque numbers by a factor of 2. In the case of PC from young male mice, actinomycin D in concentrations above 0.01 microg/ml caused reductions down to < 2% of control values in plaque counts, and puromycin (10 microg/ml) had a similar effect. The PC from retired breeder mice occupied an intermediate position between the two cases just discussed. A compartment of cells, equal to about one-fifth of the total normal PFC compartment, was identified as resistant to high concentrations of either actinomycin D or puromycin, being similar in these respects to PFC from spleens of intentionally preimmunized mice. The mitotic poison, Colcemid, did not affect plaque counts in any situation tested. The theoretical implications of these results are briefly discussed.

In vitro stimulation of antibody formation by peritoneal cells. I. Plaque technique of high sensitivity enabling access to the cells

An improved method for the short-term culture of mouse peritoneal cells in a medium containing carboxymethylcellulose (CMC), sheep erythrocytes (SRBC), and guinea pig complement is described. It involves preparation of microcultures, of thickness 12-15 micro and volume 3.6 microl, under paraffin oil. With such cultures, peritoneal cells from normal, unimmunized young male CBA mice give about 3000 hemolytic plaques per million cells cultured, this figure being attained within 24 hr. The plaque detection method is about four times as sensitive as the Jerne technique. A method is described whereby such plaque-forming cells (PFC) can be transferred, by micromanipulation, to fresh monolayer cultures containing SRBC, CMC, and complement. In this fashion, the secretory capacity and susceptibility to inhibitors of peritoneal PFC can be tested in detail. Using this technique, evidence is presented that the hemolytic substance responsible for plaque formation is actually secreted by the cell at the center of the plaque, and is not a complement component but probably an antibody. Studies on the time of plaque appearance after cell transfer, and the subsequent growth rate of the zone of hemolysis, have been performed. They speak against the idea that the PFC is either a reservoir of cytophilic antibody or a "background" PFC. Rather they suggest that active antibody secretion is induced in the cell at some defined time point in culture. Detailed kinetics of the rate of appearance of plaques in peritoneal cell cultures revealed an exponential phase lasting from about 3 to about 13 hr with a doubling time of 2 hr. The reasons for this are not known. A greatly heightened reactivity was shown in peritoneal cells of mice that had been pregnant several times. Cultures of such cells showed more rapid plaque appearance and a peak activity about 20 times higher than with cells from young male mice. Cultures in which 1 cell in 10 formed a plaque were not infrequent. A series of experiments on germ-free mice showed reactivity similar to that of conventional mice from the same strain and source. The significance of the findings for cellular immunology are discussed.

In vitro induction of a primary response to the dinitrophenyl determinant

Primary antibody response against the dinitrophenyl group has been elicited in vitro after the stimulation of normal mouse spleen explants with 2,4-dinitrophenyl (DNP)-hemocyanin or alpha-DNP-poly-L-lysine (PLL). Antibodies were detected in the culture medium by the inactivation of DNP-T4 phage. The specificity of the reaction was manifested by the lack of the capacity of the medium to inactivate the unmodified bacteriophage and by the inhibition of the inactivation of DNP-T4 with DNP-lysine.

Maturation of hemolysin-producing cell clones. I. The kinetics of the induction period of an in vitro hemolysin response to erythrocyte antigen

INVESTIGATIONS OF THE INDUCTION PERIOD OF AN IN VITRO HEMOLYSIN RESPONSE TO SHEEP ERYTHROCYTE ANTIGEN REVEALED THE FOLLOWING: 1. After antigen stimulation precursors of plaque-forming cells rapidly maturate to the point of hemolysin production. 2. Initial maturation probably occurs in the absence of cell division. 3. After initial maturation, a latent period of about 12 hr occurs before the first doubling of PFC. 4. At least the first three cell doublings are synchronous, with a generation time of 7-8 hr. 5. Synchronous cell division implies that all precursor cells are at the same point in the cell cyde when they are initially stimulated.

Lung alveolar histiocytes engaged in antibody production

After introduction of antigen (sheep red blood cells) into rabbit lung alveoli by intrapulmonary or intratracheal injection antibody forming and releasing cells are found in subsequently evoked alveolar exudates. Intratracheal immunization results in slightly delayed antibody formation with a remarkably low involvement of mediastinal lymph nodes. At peak appearance of plaque-forming cells (PFC) in alveolar exudates 20–26 per cent of PFC are histiocytes or monocytes by microscopic and ultrastructural criteria. Plaque-forming histiocytes are less differentiated forms, different from typical macrophages. Their antibody production is sensitive to puromycin and to a lesser degree to actinomycin-D. In contrast to lymphoid PFC, some of these histiocytes are sensitive to a phagocyte-destructive agent-silica. Among the PFC, plasma cells and (early after immunization) activated lymphocytes and blasts are conspicuous in comparison with the overall composition of the cell populations of the alveolar exudate and mediastinal lymph node. It is calculated that 1 in 100–500 plasma cells and 1 in 20,000–100,000 histiocytes give demonstrable haemolysin formation during the peak of cellular response. This is suggested as the difference between the specialized and occasional or `primitive' antibody forming cell.

Immune responses in vitro. I. Cellular requirements for the immune response by nonprimed and primed spleen cells in vitro

A cell suspension culture system combined with a procedure which separates most macrophages from lymphoid cells was used to investigate some of the cellular requirements for direct and indirect plaque-forming cell responses by nonprimed and primed mouse spleen cells in vitro. The plaque-forming cell response to heterologous erythrocytes in cultures of nonprimed spleen cells required both macrophages and lymphoid cells for its development. A significant indirect plaque-forming cell response did not develop in cultures of nonprimed spleen cells. In contrast, cultures of separated or macrophage-poor lymphoid cells from primed mice exhibited increasing responses relative to the response of unseparated spleen cells as the interval after priming increased. The cultures of separated lymphoid cells were not entirely free of phagocytic cells. Despite some evidence which suggests that these phagocytic cells had little function in the response, one cannot ascertain whether the lymphoid cells were responding directly to a second contact with antigen or whether the few contaminating phagocytic cells were performing a function essential to the response by the lymphoid cells. Physiologically different populations of cells appear to develop after priming and are able to respond in vitro in a macrophage-poor culture. Some of the properties of these populations suggest that they are "memory cell" pools containing precursors of direct and indirect plaque-forming cells highly susceptible to a second antigenic stimulus.

Haemolytic activity of mouse peritoneal exudate cells in vitro

Mouse peritoneal exudate cells, and to a lesser degree spleen cells, can cause haemolysis of both syngeneic and allogeneic mouse red blood cells in vitro whereas lymph node and tumour cells are ineffective. The reaction was clearly detectable after 0.5–1 hour, and is usually complete after 5–6 hours at 37°. An analogous reaction was found also with sheep red blood cell targets, but haemolysis was weaker and a significant effect was not obtained until 24 hours later. The degree of haemolysis did not increase after the addition of complement. Hemolysis was not potentiated when specifically sensitized cells were employed or when PHA was present. Viability and active metabolism of the PE cell was essential for haemolysis. Only red blood cells were affected by the PE cells, nucleated target tumour cells being resistant. It was concluded that macrophages were responsible for haemolysis, which was not mediated by antibody and complement, but represented an active macrophage reaction unrelated to previously known mechanisms of haemolysis in vitro.

Cell interactions in the primary immune response in vitro: a requirement for specific cell clusters

Mouse spleen cells were found to associate in cell clusters during the primary immune response to sheep erythrocytes in vitro. About 10% of the cell clusters had the following unique properties; (a) they contained most, if not all, antibody-forming cells, (b) they contained only cells forming antibody to one antigen when cell cultures were immunized with two antigens, (c) the cells in clusters reaggregated specifically after dispersion, and (d) the specific reaggregation of clusters appeared to be blocked by antibody to the antigen. The integrity of cell clusters was required for the proliferation of antibody-forming cells, and prevention of clustering by mechanical means or by excess antibody blocked the immune response. Antibody and antigenic determinants on the surfaces of cells probably provide the basis for interaction. The unique microenvironment of cell clusters was essential for the primary immune response in vitro.

Depressed cellular formation of antibody to Shigella antigens in vitro by spleen cell cultures from unresponsive mice

Specific antibody plaque-forming cells (PFC) to Shigella-soluble antigen did not appear in spleen cell cultures from Shigella-tolerant mice, as occurred with similar cultures prepared from normal mice immunized with Shigella antigen prior to sacrifice. Cultures from tolerant mice also failed to form serologically detectable amounts of agglutinins in vitro. Exposure of cell cultures from tolerant mice in vitro to additional antigen had little or no effect on appearance of plaque-forming cells to Shigella. Spleen cells from normal control mice formed readily detectable levels of antibody, as well as specific antibody plaque-forming cells, after similar stimulation with antigen either in vivo or in vitro. The absence of antibody-forming cells in cultures prepared from spleens of tolerant mice was specific since such cultures, as well as those from normal control mice, formed numerous antibody plaques to unsensitized sheep erythrocytes in vitro after in vivo challenge of the mice with sheep erythrocytes. Tolerance to Shigella antigen, as assessed by absence of antibody-forming cells in vitro, persisted for several months. Spleen cell cultures from tolerant mice less than 3 to 4 months of age did not form significant numbers of antibody plaques, even after in vitro exposure to specific antigen. However, spleen cultures prepared from neonatally treated mice, approximately 6 to 8 months old, formed essentially normal numbers of specific PFC in vitro, indicating that the animals had "recovered" from tolerance and that their lymphoid cells were capable of responding to Shigella antigen in vitro. Absence of specific PFC in cell cultures from tolerant animals supports the concept that tolerance is due to a central failure of specific immunocompetent cells and not due to an inhibitory effect caused by either "excess" antigen or humoral antibody.

The immune response to sheep erythrocytes in the mouse. II. A study of the cytological events in the draining lymph node utilizing cellular imprints

The cytological events of the primary and secondary immune response in the popliteal lymph node of Swiss White mice were studied following administration of sheep erythrocytes into the hind footpad. Four morphological features of cellular activity of immunologically competent cells—basophilia, synthesis of RNA, mitotic activity and distinctive cellular morphology—were analysed, and correlated with previous studies of 19S and 7S antibody forming cellular activity employing plaque assays performed on the residual lymphoid tissue remaining after production of node imprints.

The findings support the view that 19S and 7S antibody forming cells in the primary immune response are derived from two populations of cellular precursors. It is suggested that the lymphoid cell producing 19S immunoglobulin arises by transformation from the reticular cell following activation by antigen, while the 7S antibody forming cell arises from the small lymphocyte following some degree of initial transformation and subsequent cellular proliferation. The possibility that the 7S antibody forming cells had passed through a transient period of biosynthesis of 19S antibody was suggested in the present studies. Finally, evidence was provided for the presence of two morphological types of plasma cells, which, by virtue of their appearance at different stages of the primary immune response, could represent cells producing different immunoglobulins at varying rates of protein biosynthesis.

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.

Effect of phytohaemagglutinin on the immune response

The effect of phytohaemagglutinin (PHA) on the immune response of mice and rats has been investigated. A marked depression of anti-sheep erythrocyte agglutinin titres was found in both species following primary immunization. The decrease in titre was due to a depression of 2-mercaptoethanol resistant antibodies. The treated rats also developed antibodies against the haemagglutinating component of PHA.

PHA produced no depression of the delayed hypersensitivity response to tuberculin; nor did it suppress adjuvant arthritis in the rat. Histological examination of the lymphoid organs of PHA treated mice revealed reactive hyperplasia. Similar histological changes were seen in mice injected at the same time with a strong antigen such as horse ferritin. The depressive effect of PHA on IgG antibody formation and the absence of an effect on IgM antibody formation, delayed hypersensitivity, and adjuvant arthritis are discussed.