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

The compartmentalization of antigen-reactive lymphocytes in desensitized guinea pigs

A single injection of ε,DNP-Lys_7–10 can render previously sensitized guinea pigs specifically unreactive to subsequent intradermal challenge with that antigen. Antigen-reactive lymphocytes, as assayed by macrophage-migration in-inhibition or thymidine incorporation, were depleted from the peritoneal exudates of those animals. In contrast, it was intriguing to find that lymph node lymphocytes from such animals responded normally in the antigen-induced thymidine incorporation assay. These studies demonstrate a compartmentalization of antigen-reactive lymphocytes in desensitized animals which may account for the short-lived nature of this phenomenon.

Temporal changes in the distribution of thoracic duct lymphoblasts to synovium and other tissues of rats with adjuvant-induced arthritis

The distribution of lymphoblasts(lymphocytes in cell cycle) obtained from the central lymph of donor rats and transferred adoptively to syngeneic recipients has been shown previously to be influenced by the presence of arthritis in either donor or recipient rats. The intent of the present study was to examine patterns of distribution of lymphoblasts in the early period after transfer, when extravasation of donor lymphoblasts was expected to occur. Thoracic duct lymphoblasts labelled in vitro with [125I]-iododeoxyuridine were detected in recipient rats by external radiometry and autoradiography. Irrespective of donor status, fewer donor lymphoblasts accumulated in the feet of normal recipients when compared to arthritic recipients at 15 min, 2 h and 24 h after cell transfer.When recipients of similar disease status were compared, the percentages of injected lymphoblasts from normal and arthritic donors recovered in the feet were similar at 15 min and 2 h after transfer. The proportions of lymphoblasts recovered in the feetat 24 h after injection declined in normal recipients and arthritic recipients of cells from normal donor rats. Importantly,this decline did not occur when both the donor and the recipient were arthritic. In the hindpaws, donor lymphoblasts were located predominantly in the bone marrow, except in transfers between arthriticrats, when at 24 h they were predominantly in the synovium. At 15 min, lymphoblasts were detected within the lumen of vessels within synovium, whereas by 2 h extravasation of these cells was evident. In conclusion, lymphoblasts accumulate more readily in hindfeet that are inflamed. In the early hours after injection, lymphoblasts from normal and arthritic donors are recruited equally, but these early levels are only maintained for 24 hin the combination of arthritic donor and arthritic recipient. Adramatic change in the proportion of lymphoblasts located in synoviumat this later time suggests that a dynamic process of relocation,retention and/or local cell division maintains the numbers of arthritic donor cells in the latter combination.

The CD44-initiated pathway of T-cell extravasation uses VLA-4 but not LFA-1 for firm adhesion

Leukocytes extravasate from the blood in response to physiologic or pathologic demands by means of complementary ligand interactions between leukocytes and endothelial cells. The multistep model of leukocyte extravasation involves an initial transient interaction ("rolling" adhesion), followed by secondary (firm) adhesion. We recently showed that binding of CD44 on activated T lymphocytes to endothelial hyaluronan (HA) mediates a primary adhesive interaction under shear stress, permitting extravasation at sites of inflammation. The mechanism for subsequent firm adhesion has not been elucidated. Here we demonstrate that the integrin VLA-4 is used in secondary adhesion after CD44-mediated primary adhesion of human and mouse T cells in vitro, and by mouse T cells in an in vivo model. We show that clonal cell lines and polyclonally activated normal T cells roll under physiologic shear forces on hyaluronate and require VCAM-1, but not ICAM-1, as ligand for subsequent firm adhesion. This firm adhesion is also VLA-4 dependent, as shown by antibody inhibition. Moreover, in vivo short-term homing experiments in a model dependent on CD44 and HA demonstrate that superantigen-activated T cells require VLA-4, but not LFA-1, for entry into an inflamed peritoneal site. Thus, extravasation of activated T cells initiated by CD44 binding to HA depends upon VLA-4-mediated firm adhesion, which may explain the frequent association of these adhesion receptors with diverse chronic inflammatory processes.

Requirement for CD44 in activated T cell extravasation into an inflammatory site

Leukocytes extravasate from the blood into inflammatory sites through complementary ligand interactions between leukocytes and endothelial cells. Activation of T cells increases their binding to hyaluronate (HA) and enables CD44-mediated primary adhesion (rolling). This rolling could be induced in vivo in murine Vbeta8(+) T cells in response to specific superantigen stimulation; it was initially found in lymph nodes, then in peripheral blood, and finally within the peritoneum, the original inflamed site. The migration of Vbeta8(+) cells into the peritoneal cavity was dependent on CD44 and HA, as shown by inhibition studies. Thus, CD44-HA interactions can target lymphocytes to specific extralymphoid effector sites.

High antigen reactivity in mononuclear cells from sites of chronic inflammation

Antigen-specific in-vitro responses of mononuclear cells from synovial fluid and peripheral blood of patients with rheumatoid arthritis were compared with those of mononuclear cells from pleural exudate and peripheral blood of non-rheumatoid-arthritis patients with chronic pleuritis not caused by tuberculosis. The antigens tested were an acetone-precipitable fraction of Mycobacterium tuberculosis (AP-Mt), an Escherichia coli lysate containing the 65 kD heat-shock protein of M bovis BCG (65 kD/E coli), the M bovis heat-shock protein alone (65 kD), and E coli alone. The mean proliferative responses to AP-Mt were higher in synovial-fluid than in peripheral-blood mononuclear cells in rheumatoid arthritis patients (mean [SEM] stimulation index 10.5 [3.1] vs 2.6 [0.9]) and in pleural-exudate than in peripheral-blood mononuclear cells in the pleuritic patients (7.5 [1.7] vs 3.5 [2.0]). The same pattern was seen for the other three antigens. Only 1 of 26 synovial-fluid mononuclear cell samples from rheumatoid arthritis patients showed a positive response (stimulation index 3 or more) to 65 kD compared with 5 of 22 pleural-exudate mononuclear cell samples, so 65 kD seems not to be the major antigen recognised by synovial-fluid T cells in rheumatoid arthritis. Enhanced reactivity against mycobacterial and other bacterial antigens is not restricted to mononuclear cells from chronically inflamed joints but seems to be a common feature of chronic inflammation.

Endotoxin-mediated necrosis and regression of established tumours in the mouse. A correlative study of quantitative changes in blood flow and ultrastructural morphology

The fractional distribution of cardia output was measured in tumour-bearing mice treated with 50 micrograms intravenous endotoxin, and correlated with ultrastructural changes in tumour morphology. The proportion of the cardiac output going to the tumour decreased to less than 50% of its original value by 2 h and to 10%-30% by 6 h after giving endotoxin. Because endotoxin decreases absolute cardiac output, the actual perfusion of the tumour will be considerably less than these figures suggest. The decrease in perfusion correlated closely with changes in vascular morphology. Venous congestion on the tumour edge started within 1 h of giving endotoxin and by 3 h, endothelial damage and platelet aggregates were visible. At this time, all cells, tumour, connective tissue and infiltrate in the tumour centre were dead or damaged. By 24-48 h a conspicuous infiltrate of neutrophils and macrophages was present on the edge of the tumour and many of these cells were closely related to tumour cells. We suggest that the haemorrhagic necrosis may be caused by vascular obstruction leading to hypoxia and that the subsequent regression is mediated by activated macrophages and perhaps by neutrophils.

Extravascular immune complexes in experimental mycobacterial BCG granulomas

Quantitative results of Mycobacterial BCG antigen, immunoglobulin and complement in rat skin lesions during the evolution of the granuloma reveal peak values of these factors at 49 days. The combination of antigen, Ig and complement, present extracellularly and in polymorphs at this time, indicates immune complex formation at an antigen-antibody ratio which may approximate to equivalence. This development coincides with mass lysis of host macrophages, and is followed by a sharp reduction in the antigen load. At 8 mth, surviving bacilli are coated with antibody and complement, and sequestrated in activated macrophages. It is possible that this antibody is non-specific and protective to the bacilli, leading to a second multiplication of organisms. But by 1 yr and 8 mth all the bacilli are dead, and immunoglobulins and complement are at very low levels. Although immune complex deposition and macrophage lysis was not associated with complete elimination of bacilli, it marked a turning point in the infection when the bacterial load was high and cell mediated immunity (CMI) was lacking. CMI may be important, especially at low antigen levels, but the crucial role here appears to have been played by complexed antibody. These experimental findings parallel those in human cutaneous leishmaniasis. They may explain some forms of necrosis in this condition and in tuberculosis.

Time course of antilisterial activity by immunologically activated murine peritoneal macrophages

Murine peritoneal macrophages were rapidly rendered listericidal after exposure to lymphokine-rich supernatants (LRSs) derived from antigen-pulsed Listeria monocytogenes-immune spleen cells. A 6-h incubation period with LRSs was sufficient to induce microbicidal activity in resident macrophages. In vitro induction of macrophage listericidal activity by constant exposure to LRSs persisted for 18 h, after which time spleen cell factors were no longer capable of modifying intracellular inactivation of Listeria. Results obtained by utilizing a short assay indicated that the killing kinetics is extremely rapid, with large numbers of bacteria destroyed during the first 15 min of infection. Intracellular killing at this time appeared to be greatly dependent upon the stage of growth from which the microorganisms were harvested. Induction of bactericidal macrophages by infection of mice with a sublethal dose of virulent Listeria cells and subsequent intraperitoneal elicitation with heat-killed homologous bacteria was similarly a transient event. Macrophages harvested 18 h after antigenic challenge displayed dramatic antibacterial activity during the first 22 h in culture. After 22 h, activity was lost, and stasis was observed during the ensuing 23 h. At 68 h, macrophages were devoid of antilisterial action. Activity, however, could be recalled after incubation with LRSs.

Short lived, dividing cells mediate adoptive transfer of immunity to Trichinella spiralis in mice. II. In vivo characteristics of the cells

The in vivo characteristics of mesenteric lymph node cells (MLNC) capable of mediating the adoptive transfer of immunity to Trichinella spiralis have been examined. Mediator cells were diverted into the peritoneal cavity of infected donor mice following the induction of a peritoneal exudate and its was shown that these were nylon-wool, non-adherent (T) cells. After density gradient separation of [125I]-UdR-labelled MLNC, the fractions that were most effective in transferring immunity were those containing a small proportion of cells but the largest proportion of incorporated activity. Treatment of the donors of MLNC with the mitotic inhibitor vinblastine effectively prevented both the transfer of immunity and increased incorporation of [125I]-UdR characteristic of the mediator population. In vitro irradiation of MLNC failed to affect their ability to transfer immunity. Collectively these findings support the conclusion that mediator cells are T lymphoblasts, and suggest that mediation of immunity is effected directly by this population and not by their progeny.

Carbohydrate surface constituents of T cells mediating delayed-type hypersensitivity that control entry into sites of antigen deposition

Peritoneal exudate T lymphocytes (PETLs) that mediate delayed-type hypersensitivity (DTH) to sheep red blood cells in mice were modified by in vitro treatment methods which modify surface carbohydrate constituents. Neuraminidase treatment resulted in the release of both N-acetylneuraminic acid and N-glycolyl-neuraminic acid, and periodate treatment in the formation of the corresponding C7 analogues. Treatment of PETLs with neuraminidase led to a transient reduction of DTH reactions in syngeneic cell recipients. After treatment with neuraminidase plus galactose oxidase, adoptive mediation of DTH was more markedly reduced. Incubation of PETLs with periodate caused a permanent loss of DTH transferring capacity. The oxidation-induced effects following treatment of PETLs with neuraminidase plus galactose oxidase or with periodate could be reversed by subsequent reduction with borohydride of the previously formed aldehyde moieties. Decreased DTH reactions observed after the various treatment procedures were paralleled by reduced immigration of PETLs into sites of antigen deposition, indicating that the reduction/oxidation state of cell surface carbohydrates is crucial for induction of inflammatory processes by T cells. Trapping of PETLs in the liver could not be the sole mechanism since neuraminidase- and periodate-treated PETLs, but not neuraminidase plus galactose oxidase-treated PETLs, accumulated in the liver. It therefore appears that alterations in the reduction/oxidation state of the cell surface can lead to unresponsiveness of T cells to inflammatory signals.

Fate of Listeria monocytogenes in resident and activated macrophages

A sensitive and highly reproducible assay was utilized to study in vitro interactions of Listeria monocytogenes with resident and activated macrophages. The technique is not compromised by extracellular events and can readily differentiate between the efficiency of ingestion and the postphagocytic fate of bacteria. Heat-labile factors in human or homologous serum markedly enhanced the phagocytosis of Listeria without noticeably affecting the intracellular fate of the microorganisms. The behavior of Listeria within macrophages cultivated from C57BL/6 and BALB/c mouse strains corresponded to previous reports of in vivo growth patterns in inbred mice. Thioglycolate- or caseinate-elicited macrophages, although highly phagocytic, were unable to prevent the proliferation of Listeria. A bactericidal macrophage population was derived from from C57BL/6 mice which had been immunized intraperitoneally with a sublethal dose of L. monocytogenes and subsequently boosted with heat-killed homologous organisms. Elicitation of immune animals produced an increase in the percentage of peroxidase-positive macrophages, but this activity could not be correlated with restriction of intracellular bacterial growth.

Properties of peritoneal exudate lymphocytes that mediate tuberculin delayed-type hypersensitivity and anti-tuberculosis immunity

Rats were immunized with living BCG and acute peritoneal exudates were induced on the ninth day of infection. The peritoneal exudate cells (PEC), that confer adoptive anti-tuberculosis immunity and tuberculin delayed-type hypersensitivity (DTH), were subject to velocity sedimentation analysis. It was found that the ability to confer immunity of DTH was limited to a population of cells that sedimented at a rate of 3-4 mm/h. This sedimentation rate corresponds to that of small lymphocytes. No significant immunological activity was detected in large lymphocytes that incorporate [3H]-thymidine in vitro, regardless of whether the exudates were obtained 14 to 24 h after induction of peritoneal inflammation. The failure of large lymphocytes to confer immunity and DTH was not due to adherent cells with suppressor activity, because removal of adherent cells failed to amplify the transfer of immunological activity by non-adherent cells. The persistence of the ability to express immunity and DTH in adoptively immunized rats was studied. There was no decay of adoptive immunity during a 4 week period following cell transfer, but there was a rapid reduction in the expression of DTH.

Peritoneal exudate T lymphocytes with specificity to sheep red blood cells. I. Production and characterization as to function and phenotype

T lymphocytes which mediate DTH reactions to sheep red blood cells (SRBC) in mice enter casein-induced peritoneal exudates from which they can be recovered and assayed in a passive transfer system. Peritoneal exudates need not contain specific antigen for inducement of T-cell immigration. The amount (or biological activity) of DTH-transferring peritoneal exudate lymphocytes is enhanced by the previous use of immune modulating agents, such as cyclophosphamide (Cy) (200 mg/kg 2 days prior to sensitization), or BCG (10(7) live organisms i.v. 14 days prior to sensitization). SRBC-specific peritoneal exudate lymphocytes phenotypically are Thy 1+ and Ly 1+, 2-. In vivo, peritoneal exudate T cells from Cymodulated donors persist in circulation for a short period only and are subject to the suppressive mechanisms acting in anergic mice. Cells from BCG-plus-Cy-modulated donors, on the other hand, persist in circulation for a longer period and appear to be less susceptible to immune suppression.

Delayed hypersensitivity to tuberculin in rats: effects of antirheumatic drugs

The effects of different antirheumatic drugs administered according to various dosing regimes on tuberculin hypersensitivity in rats have been assessed quantitating the changes of exudate volume and mononuclear cells immigration at the site of challenge. Dosing at the time of sensitization with aurothiomalate and D-penicillamine enhanced the cell immigration which was decreased by similar treatment with levamisole. Cyclophosphamide increased the exudate formation. Indomethacin had no effect. Dosing at the time of challenge caused a marked reduction of both the parameters by aurothiomalate and cyclophosphamide and enhancement by levamisole. D-penicillamine increased only the cellular immigration and indomethacin the exudate formation. Long treatment with aurothiomalate and cyclophosphamide suppressed the responses. Similar treatment with D-penicillamine and levamisole produced a significant enhancement. Indomethacin had no effect. The relevance of these findings to the testing and mode of action of antirheumatic drugs is discussed.

Radiometric ear index test as a measure of delayed-type-hypersensitivity in the rat

Intradermal skin tests performed in the pinna of the rat ear appeared to be 100 times more sensitive than classical flank skin tests in measuring Arthus and delayed-type hypersensitivity (DTH) reactions. One of these tests was antigen-induced thickening of the pinna of the ear. It was found to be a sensitive measure of Arthus reactivity at 4 h after irritation with antigen in both actively immunized rats and recipients of precipitating immune serum. The other test, radiometric ear index determination, exploits the fact that monocytes and monocyte derived macrophages accumulate at DTH reaction sites. The test was performed by labelling the precursors of these cells with a pulse of [3H]-thymidine and by determining radioactivity in biopsy specimens taken from test sites in the pinna of the ear. At a certain antigen dose range this objective and highly sensitive method was shown to measure a purely cell mediated reaction which could be transferred to normal recipients with thoracic duct lymphocytes but not with immune serum. It also behaved as a typical DTH reacttion in response to desensitizing injections of the specific antigen. Testing with unnecessarily high antigen doses, however, should be avoided since the strong early inflammation induced by them may interfere with the determination of DTH while using this sensitive assay.

Host defenses in experimental scrub typhus: role of spleen and peritoneal exudate lymphocytes in cellular immunity

Lymphocytes obtained from spleens or peritoneal exudates of immune donor mice were evaluated for their ability to passively confer protection on recipients subsequently challenged with virulent scrub typhus rickettsiae. Peritoneal exudate lymphocytes (PELs) injected intraperitoneally were able to transfer complete protection against rickettsial challenge by 5 days after immunization, whereas splenic lymphocytes (SpL's) required 15 days to exhibit similar resistance. When immune lymphocytes were transferred intravenously, cells from both anatomical compartments required 15 days after immunization before they were able to completely protect recipients. PELs maintained this protective capacity for 2 weeks, but the passive immunity induced by intravenously transferred SpL's rapidly diminished to insignificant levels. It was particularly interesting that the protective effect of SpL's could be dramatically reduced by the concomitant presence of a mineral oil-induced peritoneal exudate. Almost total abrogation of resistance was observed when SpL's obtained from exudate-bearing mice were transferred intravenously. The protective capacity of both PELs and SpL's was resistant to 1,200 rads of gamma radiation at 7 to 10 days after immunization, but resistance was transient and by 3 weeks was undetectable. It was not possible to determine from this study whether the transferred lymphocytes were proximate mediators of protection in scrub typhus infection of mice or whether they served to recruit the host's own defenses, or both. However, it was possible to conclude that PEL's and SpLs exhibited functional heterogeneity and that PELs were more efficient mediators of protection.

Adoptive transfer of immunity from mice immunized with ribosomes or live yeast cells of Histoplasma capsulatum

This investigation was designed to compare the role of lymphoid cells and immune serum in protective immunity induced by immunization with ribosomes or live yeast cells of Histoplasma capsulatum. Spleen cells, peritoneal cells, and serum from C3H mice immunized with Histoplasma ribosomes or live cells were transferred intravenously to separate groups of syngeneic recipients. All recipients along with a set of immunized and control mice were challenged intravenously with 4 x 10(6) yeast cells of H. capsulatum, and protection was assessed. Immunization with ribosomes or live cells provided 90 to 100% protection. Mice receiving filtered spleen cells or peritoneal cells from donors immunnized with live cells showed 90 to 100% protection; 80 to 90% protection was observed for mice receiving cells from ribosome-immunized donors. In contrast, no evidence of protection was seen in mice receiving serum from either live-cell- or ribosome-immunized mice. Peritoneal cells were far more efficient than spleen cells in adoptive transfer of immunity. The adoptive immunity in recipients persisted for at least 3 weeks after transfer, the longest period tested in the present study. These results indicate that the immunity elicited by immunization with Histoplasma ribosomes or live cells is mediated by a cellular mechanism.

Antibacterial product of peritoneal exudate cell cultures from guinea pigs infected with mycobacteria, listeriae, and rickettsiae

In an in vitro model of cellular immunity, the antibacterial product of immunologically mediated mononuclear cell activation was studied from guinea pigs infected with listeriae and rickettsiae and compared with the product previously described from animals infected with mycobacteria. We found that this product, active against gram-positive bacilli, appeared to be identical in the three different infections with regard to its heat stability, its chromatographic adsorption and elution pattern, its susceptibility to inactivation by proteolytic enzymes, and its antibacterial spectrum

The mediator of cellular immunity. XII. Inhibition of activated T cells by Newcastle disease virus

Newcastle disease virus (NDV) can interact in at least two ways with rat T cells. By adsorbing to circulating lymphocytes, the virus can transiently deflect the cells from lymph nodes and inflammatory exudates induced in the peritoneal cavity. T cells are affected regardless of age, state of activation, or position in the mitotic cycle. The effect is reversible and is mediated not only by infectious (I)-NDV, but also by UV-NDV which cannot achieve a complete replication cycle in eggs. But I-NDV has another lasting effect on activated T cells. It is revealed in the failure of virus-treated thoracic duct lymphocytes to transfer cellular resistance to Listeria monocytogenes, delayed-type hypersensitivity to soluble antigens of the parasite, and the permanent exclusion of labeled S-phase lymphocytes from inflammatory foci. Activated T cells are inhibited by virus multiplicites which have little if any effect upon the proliferative potential of antigen-sensitive T cells or localization of labeled small lymphocytes in lymph nodes. The underlying mechanism has not been determined; however, there are reasons for thinking that NDV has a lethal effect upon activated T cells, because the latter are permissive for virus replication.

Mononuclear cell turnover in chronic inflammation: studies on tritiated thymidine-labeled cells in blood, tuberculin traps, and dermal BCG lesions of rabbits

Rabbits were injected intradermally in multiple sites with BCG. Four days after the BCG injection, they were injected intravenously with a single pulse of tritiated thymidine (3H-TdR) at various times thereafter, the BCG lesions were biopsied and evaluated for 3H-TdR-labeled mononuclear cells (MN). Periodically, Old Tuberculin (OT) was injected intradermally, creating MN traps which were biopsied and evaluated 1 day after their onset. 3H-TdR-labeled cells were also evaluated in samples of blood. During the first 8 days after the 3H-TdR pulse, the labeled MNs represent short-lived cells, i.e., recently dividing monocytes and lymphocytes. During this time, the percentage of labeled MNs in the blood, in the traps, and in the BCG lesions rose and fell together. This result suggests that the majority of the MNs in the BCG lesions had a turnover rate of about a week. By 12 days and afterward, the percentage of MNs labeled by 3H-TdR in the blood was higher than that in the BCG lesions which was in turn higher than that in the traps. At this time the circulating MN population probably contained labeled long-lived lymphocytes that did not enter inflammatory sites (the traps) as readily as the short-lived lymphocytes. The labeled MNs remaining in the BCG lesions probably did not divide and dilute out their 3H-TdR label as readily as those that were trapped from the bone marrow via the blood. The percentage of MNs labeled with 3H-TdR in the traps had decreased to about one-fifteenth of its peak value by 12 days, suggesting that the bone marrow's supply of labeled MNs was depleted at this time, except for the few cells labeled as a result of 3H-TdR reutilization.

Transfer of adoptive immunity to tuberculosis in mice

A system is described for studying adoptive immunity to tuberculosis in syngeneic mice. Donor mice were immunized with 10(4) BCG intravenously, and lymphoid cells were harvested 28 days later. Adoptive immunity was measured in recipient mice in terms of the inhibition of growth of BCG in the liver and spleen following intravenous injection. Adoptive immunity was expressed optimally when recipients were sublethally irradiated (500 R), challenged with 10(4) to 10(5) viable organisms, and given sensitized lymphoid cells intravenously. Adoptive immunity was not manifest until 14 days after challenge and was effective against Mycobacterium tuberculosis H37Rv as well as BCG. Immunity could be conferred by spleen, lymph node, peritoneal exudate, and resident peritoneal (washout) cells. The lymphoid cells conferring immunity were shown to be thymus-dependent lymphocytes by virtue of their nonadherence to glass wool and sensitivity to anti-theta serum plus complement. The sensitized cells were relatively susceptible to both in vitro and in vivo X-irradiation.

Immunity in acute bacterial infections

A brief survey of the ways in which humoral and cellular immune responses deal with bacteria and their products shows that a variety of effector mechanisms is involved. Their efficiency varies, partly in relation to the kind of bacterial attack with which they have to deal. Some bacterial factors though not crudely toxic can interfere with specific host defences.

The migratory behavior of T blasts to contact sensitivity reactions in activelyand passively sensitized mice

The arrival of cells from lymph nodes immunized with the contact sensitizing agents oxazolone and picryl chloride at ears challenged with these antigens was studied inmice using the technique of labelling with -51Cr. An apparent specificity of arrival was seen because the immune cells transfered contact sensitivity passively, giving rise to an inflammatory response in the ear, to which a subpopulation of cells (T blasts) was non-specifically attracted. It was also shown that there are at least two distinct populations of cells with the ability to move to inflammatory sites: the first, found in immunized lymph nodes, moves to contact sensitivity reactions in both actively and passively sensitized mice; the second, found in bone marrow and oil-induced peritoneal exudates, moves to contact sensitivity reactions in actively sensitized mice, whereas in passively sensitized mice, the arrival of these cells at contact sensitivity reaction is poor. It is suggested that the ability of T blasts to move to sites of inflammation my be useful as an assay technique for contact sensitivity reactions.

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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.

Cell-mediated immunity against Besnoitia and toxoplasma in specifically and cross-immunized hamsters and in cultures

The capacity of hamster peritoneal cell populations to control viability and growth of Besnoitia and Toxoplasma organisms was assessed in vivo and in vitro. Immunized hamsters reduced the homologous organisms 100- to 10,000-fold over a 5-day period, but the heterologous infection increased 100- to 1,000-fold in numbers, similar as in the nonimmune controls. Passively administered antibody was ineffective although lytic cofactors were supplied by hamsters. In cultures, peritoneal cells from Besnoitia-immune hamsters delayed the growth of homologous parasites to an average of 38.5 h per division; however, in Toxoplasma-immune and nonimmune cells, Besnoitia divided every 12.8 h. Specificity of immunity was pronounced against both infections. With cross-infections, Toxoplasma-immune cultures did not effectively delay Besnoitia growth; however, Besnoitia-immune cultures reduced Toxoplasma growth by one-half. Co-cultivation experiments demonstrated that specifically committed lymphocytes could instruct macrophages to reduce the homologous organism 10-fold, whereas heterologous organisms were reduced only 2-fold. Lymphocyte supernatants initiated hypersensitivity as indicated by macrophage activation and giant cell formation in culture. However, these supernatants did not transfer infection immunity. Lymphokines could account for the hypersensitivity phenomena, but cell-mediated infection immunity in this model required close lymphocyte-macrophage proximity. These studies indicate that a number of distinct processes including delayed hypersensitivity, macrophage activation, and specific cellular immunity are acting simultaneously during latent Besnoitia infection of hamsters. All three processes are mediated by lymphoid cells and appear to be specifically induced. Although activated macrophages develop some heightened nonspecific capabilities, these were several orders of magnitude below the specific effects.

Contact sensitivity in the mouse. XI. Movement of T blasts in the draining lymph nodes to sites of inflammation

An earlier paper showed that 4 days after immunization with the contact sensitizing agent `oxazolone' there is a peak in the percentage of cells in the draining lymph nodes that move to sites of inflammation. This was assessed by dissociating the lymph nodes, labelling them with ⁵¹Cr and injecting them into mice whose ears were painted within an hour with an unrelated contact sensitizing agent or with croton oil. The ears were then removed at about 18 hours and their radioactivity used as a measure of cell arrival.

The cells that move to sites of inflammation are not macrophages as they are not removed by filtration through cotton wool. They are θ-positive and control studies show that the activity of the anti-θ serum was indeed due to antibody to the θ-antigen. The cells are large and can be labelled both in vivo and in vitro with [¹²⁵I]-iododeoxyuridine which is incorporated the DNA of cells during the S phase of the cell mitotic cycle. It was concluded that the cells in immunized lymph nodes that move to sites of inflammation are T blasts. The unitary hypothesis is put forward that following immunization for delayed hypersensitivity a particular class of T cells proliferates and gives rise to large pyroninophilic blast cells; and that these cells or their immediate descendants possess the properties, either at the same time or at closely related times, of movement to sites of inflammation and non-specific cytotoxicity as well as the capacity to passively transfer cellular immunity.

Contact sensitivity in the mouse. X. Non-specific cytotoxicity of T blasts in the draining lymph nodes

CBA mice were immunized by painting the skin with the contact sensitizing agent `oxazolone'. The draining lymph nodes were taken at 4 days and mixed with <sup>51</sup>Cr-labelled mastocytoma tumour cells. Cytotoxic killing was assessed by the release of <sup>51</sup>Cr. Little killing occurred in the absence of phytohaemagglutinin. However, immunized but not normal lymph node cells killed the mastocytoma cells providing phytohaemagglutinin (PHA) was present during the killing reaction. Analysis by the `one hit' hypothesis suggested that up to 14 per cent of the lymphocytes in immunized lymph nodes were effector or killer cells.

The cytotoxicity was non-specific. The evidence for this was that DBA/2 lymph nodes immunized with oxazolone killed DBA/2 mastocytoma cells. The killing reaction did not require macrophages but was due to large cells. These were shown to be θ-positive in carefully controlled experiments. The non-specific cytotoxicity was greatest 4 days after immunization with oxazolone. Reimmunization of the mice on day 10 did not cause a classical secondary response, as assessed by non-specific cytotoxic killing. Instead the time course resembled the primary while the magnitude of killing was slightly reduced.

There were several similarities between non-specific cytotoxic cells and the large pyroninophilic cells and the cells which move to sites of inflammation which are found in lymph nodes immunized with contact sensitizing agents. These similarities included θ-positivity, large size and peak occurrence 4 days after immunization. It is postulated that non-specific cytotoxicity and movement to sites of inflammation are due to blasts or their immediate descendants which originated from T lymphocytes.

Specificity of a BCG-induced pulmonary granulomatous response in rabbits

The specificity of Bacillus Calmette Guérin (BCG)-induced accelerated pulmonary granuloma formation has been evaluated in rabbits by cross sensitization-challenge experiments by using another granulomagenic organism, Corynebacterium granulosum. BCG-sensitized rabbits responded to challenge with homologous but not heterologous antigen, indicating that BCG-induced accelerated granuloma formation displays specificity characteristic of immunological reactions. These differences were also observed in local pulmonary delayed hypersensitivity, as determined by the migration inhibition test. The relationship between local pulmonary delayed hypersensitivity and the accelerated granulomatous response is discussed.

Relationship of BCG-induced pulmonary delayed hypersensitivity to accelerated granuloma formation in rabbit lungs: effect of cortisone acetate

The role of local pulmonary delayed hypersensitivity in accelerated pulmonary granuloma formation was investigated using cortisone acetate, an immunosuppressive drug that appears to preferentially eliminate committed lymphocytes at appropriate doses. Data are presented showing that cortisone acetate suppressed local pulmonary delayed hypersensitivity at the time of and subsequent to challenge with BCG. Furthermore, cortisone damage appeared to involve primarily committed lymphocyte populations since the defect was repairable with sensitized spleen cells, an unlikely source of macrophage precursors.