Radioautographic studies of small lymphocytes in the thoracic duct of the rat

Characteristics of Cell Proliferation in Children's Lymphoblastic Leukemia

The proliferative activity of the bone marrow and peripheral cells of acute infant lymphoblastic leukemia was evaluated by « in vitro » incorporation of thymidine-H3. The proliferative activity of leukemic lymphoblasts proved roughly similar to that already observed in hemocito-myeloblastic acute leukemias of adults. Within the lymphoblastic population, incorporation of tritiated thymidine was distributed very heterogeneously and there was no labelling of the smaller blasts. In the larger blasts, the labelling index increased progressively with the increase in cell diameter. The acute leukemia population can thus be divided into two classes: proliferating and non-proliferating. A study of the proliferative activity of lymphoblasts, contemporaneously in bone marrow and peripheral cells, suggested a division of cases into two groups. In one proliferative activity in the marrow was greater than in the peripheral blood; in the other it was equal to or less than in the peripheral blood. The second group was made up of cases whose clinical features presented a much more marked hepato-splenomegaly and high peripheral leucocytosis. A more detailed study of proliferative activity considering various classes of blasts within the same population showed that, in the first group of patients, the highest percentage of large blast cells is found at bone marrow level, while in the second the percentage of large blasts in the marrow is equal to or less than that observed in the peripheral blood. It was also shown that total proliferative activity is correlated to the percentage of large blasts. On the basis of these findings, one may admit that in first group forms the leukemia cells are generated prevalently in the bone marrow, while in second group forms most leukemic cells are formed elsewhere.

Subpopulations of long-lived and short-lived T cells in advanced HIV-1 infection

Antigenic stimulation of T cells gives rise to short-lived effector cells and long-lived memory cells. We used two stable isotope-labeling techniques to identify kinetically distinct subpopulations of T cells and to determine the effect of advanced infection with HIV-1. Long-term deuterated water (2H2O) incorporation into DNA demonstrated biphasic accrual of total and of memory/effector (m/e)-phenotype but not naive-phenotype T cells, consistent with the presence of short-lived and longer-lived subpopulations within the m/e-phenotype T cell pool. These results were mirrored by biphasic die-away kinetics in m/e- but not naive-phenotype T cells after short-term 2H-glucose labeling. Persistent label retention was observed in a subset of m/e-phenotype T cells (presumably memory T cells), confirming the presence of T cells with very different life spans in humans. In advanced HIV-1 infection, much higher proportions of T cells were short-lived, compared to healthy controls. Effective long-term anti-retroviral therapy restored values to normal. These results provide the first quantitative evidence that long-lived and quiescent T cells do indeed predominate in the T cell pool in humans and determine T cell pool size, as in rodents. The greatest impact of advanced HIV-1 infection is to reduce the generation of long-lived, potential progenitor T cells.

B- and T-lymphocyte subset numbers in the migrating lymphocyte pool of the rat: the influence of interferon-gamma on its mobilization monitored through blood and lymph

The subset composition of the migrating lymphocyte pool is largely unknown. In order to determine the number of B, T, CD8+, CD4+ and CD4+ 'naive' (CD45RC+) and 'memory' (CD45RC-) lymphocytes in this pool, the thoracic duct lymph of the rat was drained for 7 days. The effect of lymphocyte depletion on the number of blood lymphocytes was also monitored. In addition, the influence of continuously applied interferon-gamma (IFN-gamma) on the mobilization of the migrating lymphocyte pool was investigated. Within 1 week 2 x 10(9) thoracic duct lymphocytes (TDL) were collected, which represents about 50% of the total lymphocyte pool of an adult rat. Among the migrating lymphocytes an early and a late mobilized population could be differentiated. In the former the CD4+ 'naive' (CD45RC+) T lymphocytes constituted the largest population, whereas in the latter it was the B lymphocytes. Continuous infusion of IFN-gamma did not affect the number of lymphocytes in the blood. In contrast, in the thoracic duct IFN-gamma reduced the appearance of all lymphocyte subsets. However, the pattern of reduction over time differed markedly depending on the population (early or late mobilized) and the phenotype (B- or T-lymphocyte subsets). Thus, the migrating lymphocyte pool of the rat is very heterogeneous regarding its populations and shows complex changes in the mobilization pattern after IFN-gamma stimulation. Future studies should focus on how the size and the composition of the migrating lymphocyte pool is regulated.

Preferential labeling of rat lymphocytes with a rapid rate of turnover by tritiated deoxycytidine

Lymphocytes in thymic cortex and germinal centers of lymphoid tissues are labeled intensely with generally labeled tritiated deoxycytidine [G-3H]dCyd whereas they are weakly labeled with methyl tritiated deosythymidine [methyl3H]dThd of the same specific activity, not only by single injection but also by an intensive injection schedule. [G-3H]dCyd can be used to label short-lived lymphocytes strongly, although not specifically. The distribution patterns of labeled lymphocytes were different depending on the injection schedules of [G-3H]dCyd. [G-3H]dCyd can be used as a precursor molecule for cytosine and also thymine found in DNA. The ratios of radioactive thymine to crytosine measured biochemically on DNA extracted from radioactive lymphocytes labeled by the various schedules indicate strongly that short- and long-lived lymphocyte populations have different abilities to utilize pyrimidine nucleosides for DNA synthesis.

The mediator of cellular immunity. VII. Localization of sensitized lymphocytes in inflammatory exudates

Peritoneal exudates induced in rats infected with Listeria monocytogenes contain sensitized lymphocytes which can protect normal recipients against a Listeria challenge. The protective cells arise in lymphoid tissue remote from the peritoneal cavity. Those formed in the caudal lymph nodes of subcutaneously infected rats are delivered to the thoracic duct and hence to the blood from where they are drawn into exudates. Immunoblasts are the most immature members of this protective cell population and they alone among the cells in central lymph localize in exudates induced by killed bacteria. They do so in substantial numbers, but only during the early postinduction period. The "homing" of immunoblasts to inflammatory foci seems to be determined by a general property of the cells rather than their immunological commitment; however, the intense inflammation induced by organisms to which an animal has been specifically sensitized is accompanied by an exuberant influx of immunoblasts into lesions. Sensitized lymphocytes that extravasate in the inflamed peritoneal may generate more of their own kind, but some give rise to small lymphocytes. The latter also have protective properties and, with time, comprise an increasing portion of the protective cell population. The results imply that the tissue disposition of sensitized lymphocytes in the body is determined by a complementary relationship between blood-borne immunoblasts and vascular endothelium in inflamed tissue. The results also provide a plausible explanation for the concentration of sensitized lymphocytes at sites of microbial implantation where they alone would be expected to collaborate with monocyte-derived macrophages in the control of infection.

The role of lymphocytes in antibody formation. V. Transfer of immunological memory to tetanus toxoid: the origin of plasma cells from small lymphocytes, stimulation of memory cells in vitro and the persistence of memory after cell-transfer

Immunological memory to tetanus toxoid was transferred to heavily irradiated rats by thoracic duct lymphocytes (TDL) from primarily immunized donors. The recipients gen­erated substantial serum antibody responses when they were challenged with antigen and at the height of the response accumulations of specifically fluorescent plasma cells had developed in the splenic red pulp. When F 1 hybrid TDL were transferred to irradiated parental-strain animals it was possible to determine the origin of the specifically fluorescent cells in the spleen by observing the damage inflicted on them in vitro by alloantisera and com­plement. The analysis showed that all the antibody-forming cells were of donor origin; in morphological terms the experiments established that small lymphocytes develop by differentiation and division into plasma cells. Secondary responses to tetanus toxoid were also observed when TDL were incubated with antigen in vitro , washed thoroughly and then transferred to irradiated animals without further antigenic challenge. These experiments suggested that macrophages were not essential for the induction of the secondary response. Irradiated rats given TDL from immunized donors 4 weeks previously yielded, in turn, TDL capable of transferring immunological memory to further irradiated animals. This implicates long-lived lymphocytes as the carriers of memory. Further, it was shown that the secondary responsiveness conferred on irradiated animals by TDL was not diminished by chronic drainage of cells from a thoracic duct fistula, a procedure which severely depletes recirculating lymphocytes. This phenomenon has also been observed in actively immunized animals. These observations raise the possibility that recirculating memory cells may with­ draw into lymphoid tissue and become sessile for part of their life history.

Initiation of antibody responses by different classes of lymphocytes. V. Fundamental changes in the physiological characteristics of virgin thymus-independent ("B") lymphocytes and "B" memory cells

The life-span and migratory characteristics of rat thoracic duct cells which initiate the adoptive primary and secondary antibody response to diphtheria toxoid (DT) and horse spleen ferritin (HSF) were investigated. The experimental results show that thoracic duct lymphocytes from normal (unimmunized) donors are able to restore the adoptive response of irradiated hosts to HSF. Thoracic duct cells passaged through an intermediate host (intravenous injection and subsequent collection in the thoracic duct lymph) showed a marked reduction in their restorative action as compared with unpassaged cells. In addition, the restorative action of cells from donors treated with thymidine-(3)H for 48 hr before cannulation of the thoracic duct was markedly decreased. This indicates that a population of lymphocytes involved in the adoptive primary response is unable to recirculate from the blood to the lymph and is turning over rapidly (short lived). The nonrecirculating, short-lived lymphocytes are proably "B" cells, since a combination of spleen cells from neonatally thymectomized rats and passaged or thymidine-(3)H-treated cells restores a vigorous response to HSF. On the other hand, passaged or thymidine-(3)H-treated thoracic duct cells from donors immunized to DT or HSF are able to restore a vigorous adoptive secondary antibody response. Experiments with the hapten-protein conjugate, DNP-DT, show that the majority of both helper ("T") and precursor ("B") cells are able to recirculate and are slowly turning over (long lived). The findings suggest that T lymphocytes involved in both the primary and secondary antibody response are recirculating, long-lived cells. However, B lymphocytes involved in the primary response are nonrecirculating, short-lived cells ("B(1)" cells) which undergo a fundamental physiological change to recirculating, long-lived cells ("B(2)" cells) involved in the secondary antibody response.

The immunologically specific retention of recirculating long-lived lymphocytes in lymph nodes stimulated by xenogeneic erythrocytes

The lymph nodes of mice actively or adoptively immunized to sheep RBC and/or chicken RBC selectively retain long-lived lymphocytes after challenge with the appropriate antigen. This retention is demonstrable within 8 hr of the time of stimulation, though it probably begins even before this, and it is essentially complete within the first 24 hr. A similar selective retention is seen in nodes regional to the injection of some nonimmunogenic substances such as turpentine, but not others such as colloidal carbon or syngeneic RBC. In animals adoptively immunized to sheep and chicken RBC simultaneously, there is a preferential accumulation of the labeled long-lived lymphocytes of donors immunized to sheep RBC in lymph nodes challenged with sheep RBC, and a preferential accumulation of lymphocytes (labeled with a different radioisotope) from donors immunized to chicken RBC in lymph nodes challenged with this antigen. This immunologically specific component is demonstrable whether the antigen is given before or after adoptive immunization, suggesting that the only labeled cells capable of specific localization in this system are those cells that normally remain in the recirculating pool. In the present experiments, 31 out of 31 sets of antigenically stimulated lymph nodes have shown radiochemical evidence of immunological specificity in the distribution of donor lymphocytes between them, while corresponding sets of nonstimulated lymph nodes have shown only small random variations in the distribution of donor cells. Two different mechanisms are postulated whereby antigenic stimulation can alter the traffic of recirculating long-lived lymphocytes through stimulated lymph nodes. One affects recirculating cells of a particular immunological specificity, while the other affects recirculating cells without regard to their immunological specificity.

The life-span and recirculation of marrow-derived small lymphocytes from the rat thoracic duct

These experiments describe the preparation of pure marrow-derived lymphocyte suspensions from the thoracic duct of thymectomized, irradiated rats reconstituted with bone marrow cells. The majority of marrow-derived cells were small lymphocytes morphologically indistinguishable from small lymphocytes in thoracic duct lymph of normal donors. Marrow-derived small lymphocytes (B lymphocytes) were a predominantly long-lived population; the frequency of short-lived B lymphocytes in the thoracic duct was not significantly higher than the frequency of short-lived small lymphocytes in normal lymph. B lymphocytes transferred to normal recipients recirculated from blood to lymph. The first appearance of intravenously injected B lymphocytes in the thoracic duct was delayed relative to lymphocytes from normal donors and there was no clear cut modal recirculation time. Nevertheless their recirculation over a 48 hr period after transfusion was of the same order of magnitude as that of lymphocytes from normal donors.

A study of gluco-corticosteroid-induced pyknosis in the thymus and lymph node of the adrenalectomized rat

Pyknotic nuclei, observed in the thymus of steroid-treated rats, are dense, homogeneous, intensely basophilic and Feulgen positive. Under the electron microscope, the image is that of a complete segregation of the chromatin from the nuclear sap producing a margin or crescent of condensed chromatin. Approximately 30% of all small thymocytes appeared to undergo this type of degeneration within 3-4 hr after administration of the synthetic corticosteroid, dexamethasone. At this time, pyknotic thymocytes were observed in clusters, probably as a result of the activity of dense reticular cells and macrophages. Topographical and experimental data suggest the existence of a select population of steroid-sensitive thymic cells. Furthermore, on the basis of thymidine-(3)H incorporation studies, it appears that the steroid-sensitive population of thymocytes does not correspond to "aged" cells. In addition, many plasma cells became pyknotic after the same steroid treatment, indicating an unexpected similarity between their nuclei and those of lymphocytes. Finally, steroid failed to induce pyknosis of thymocytes in a variety of in vitro experiments, suggesting that the in vivo effect of steroid is of an indirect nature. The results are discussed in terms of (a) the nature of the nuclear changes characterizing pyknosis, (b) the hypothetical mechanism whereby steroids trigger such changes, and (c) the population of cells susceptible to steroid-induced pyknosis.

The mediator of cellular immunity. 3. Lymphocyte traffic from the blood into the inflamed peritoneal cavity

A substantial portion of the lymphocyte-like cells in induced peritoneal exudates derive from cells which enter the blood by way of the thoracic duct. The migrant cells have been identified as large and medium lymphocytes, but they may also include short-lived small lymphocytes derived from them. Small lymphocytes which have a potentially long circulating life-span are excluded from exudates, although cells of this type predominate in thoracic duct lymph. The results imply that many (perhaps all) of the small round cells in inflamed tissue are members of a line of rapidly proliferating lymphocytes. Specifically committed lymphocytes with precisely these properties are added to the blood of rats infected with Listeria monocytogenes. The localization of committed lymphocytes in inflammatory foci could be the crucial event which enables the host to focus his cellular defenses at sites of bacterial implantation.

Rat thoracic duct lymphocytes: types that participate in inflammation

Newly formed small lymphocytes with a short life-span in the blood are the only cells from thoracic duct lymph which accumulate in acutely inflamed tissue. This conclusion is drawn from studies in which rats with induced peritonieal exudates were injected intravenously with radioactively labeled thoracic duct cells. Radioactivity, originally vested in newly formed donor small lymphocytes, was found later in a small number of similar exudate cells. Small lymphocytes generated 10 days or more before the thoracic ducts were cannulated failed to localize in peritoneal exudates, although the cells moved in large numbers from the blood in to lymph nodes.

Review lecture. Immunosuppressive agents, with special reference to antilymphocytic serum

‘Immunosuppressive agents’ are precisely what their name implies: agents that weaken or abolish the immunological response. The term itself promises more than any agent has in fact achieved. Strictly speaking, an immunosuppressive drug or treatment should be one that inhibits the immune response and no other. A central theme of this lecture is that only antilymphocytic serum (hereafter ALS) comes anywhere near fulfilling the requirements of this definition. The immunosuppressive action of all other agents in common use is a byproduct of some much more general toxic or inhibitory influence which happens to affect, amongst many others, the cells that transact the immunological response. For this reason immunosuppressive agents have not yet begun to do for immunology what specific metabolic inhibitors have done for the analysis of cellular metabolism—to resolve a complex biological performance into separate episodes or cellular events. Our knowledge of how they work is purely empirical; it has been pieced together from the evidence of practical experience, rather than founded on a prior theoretical understanding of how they work. Immunosuppressive agents owe their importance to the sheer pressure of medical necessity. Diseases or disabilities that are due to immunological failure or insufficiency—e. g. to a congenital insufficiency of blood proteins of the class to which antibodies belong—are less common and less perplexing than those which can be attributed to a miscarriage or abnormal manifestation of the immunological response. Hay fever, asthma, urticaria and the allergies generally, including drug and bacterial allergies; anaphylaxis and serum sickness; haemolytic disease of the newborn; blood transfusion incompatibilities and that rather different form of incompatibility which prohibits the grafting of tissues from one individual to another; the so-called ‘auto-immune’ diseases, whether primary or secondary, including auto-immune thyroiditis and some of the so-called collagen diseases—all these are, to a greater or lesser degree, miscarriages or misadventures of the immunological response. There can therefore be no question of the strength of the practical incentive to bringing the immunological response under control.

Initiation of antibody responses by different classes of lymphocytes. I. Types of thoracic duct lymphocytes involved in primary antibody responses of rats

Thoracic duct cells and spleen cells were tested for their ability to restore the primary antibody response of X-irradiated rats to bovine serum albumin (BSA), sheep red blood cells (SRBC), horse spleen femtin (HSF), and Salmonella typhi flagella. Spleen cells were at least as efficient as thoracic duct cells in restoring the response to BSA, HSF, and Salmonella typhi flagella. In further experiments thoracic duct cells lacking large dividing lymphocytes were tested for their ability to restore the primary response. Large lymphocytes were eliminated by the in vitro incubation of thoracic duct cells for 24 hr at 37 degrees C or by treatment of thoracic duct cell donors with the mitotic inhibitor vinblastine sulfate 24 hr prior to cannulation of the thoracic duct. Experiments with SRBC show that incubated cells and cells from vinblastine-treated donors are as efficient as normal cells in restoring the primary antibody response. On the other hand, experiments with HSF and Salmonella typhi flagella show that incubated cells and cells from vinblastine-treated donors are about five times less efficient than normal cells in restoring the response. Normal thoracic duct cells were more efficient than incubated cells but less efficient than cells from vinblastine-treated donors in restoring the early response to BSA. The experimental findings indicate that the classes of thoracic duct lymphocytes which initiate the primary antibody response to SRBC differ from the classes which initiate the response to HSF and Salmonella typhi flagella, or BSA.

The effect of neuraminidase on the fate of transfused lymphocytes

Evidence has been obtained that incubation of rat lymphocytes with neuraminidase, prior to intravenous transfusion into allogeneic or syngeneic recipients, alters the distribution of the cells. Many enzyme-treated lymphocytes initially become trapped in the liver, and there is a decrease in the selective accumulation of these cells in the lymph nodes and spleen. Subsequently, many enzyme-altered cells emigrate from the liver, concentrate in lymph nodes, and recirculate to the lymph. The results suggest that sialic acid constituents of the lymphocyte surface play a critical role in ensuring the normal distribution of these cells in the body. The findings also imply that reactions involving surface sialic acid can markedly alter the fate of lymphocytes without "killing" the cells.

Cytology of immunologic memory. A morphologic study of lymphoid cells during the anamnestic response

Pairs of rats were immunized with keyhole limpet hemocyanin (KLH) and simultaneously labeled with thymidine-methyl-(3)H or 5-iodo-2'-deoxyuridine-(125)I. From 10-50 days later, their lymphoid organs were examined 3 days after anamnestic stimulation with KLH or after primary injection of BGG. Light and electron microscopic study of the labeled cells revealed that immunologic memory resided in the mature resting monoribosomal lymphocyte which, upon stimulation, transformed to an immature polyribosomal lymphocyte and mitotically active blast cell. These latter elements differentiated into plasma cells directly or after mitosis.

Lymphocytes: circulation altered by trypsin

Rat thoracic duct lymphocytes altered by trypsin in vitro do not circulate normally. At early intervals after transfusion of lymphocytes labeled with chromium-51 selective accumulation of radioactivity in the lymph nodes is abolished, while uptake in the spleen is not reduced. Later, the cells appear to "home" to lymph nodes and recirculate to the lymph.