Rapid colormetric assay for cell viability: Application to the quantitation of cytotoxic and growth inhibitory lymphokines

A rapid colormetric microtiter assay has been developed to detect cytotoxic lymphokines produced by human lymphocytes activated with lectins or tumor cells. The viability of lymphotoxin-treated target cells was detected using a tetrazolium dye that is reduced to a blue formazan by living but not dead cells. The amount of dye formed was quantitated using a microplate spectrophotometer (ELISA plate reader) and visual observations confirmed the amount of formazan dye produced was directly proportional to the number of viable target cells. The advantages of using this colormetric method are that it requires no washing steps or radioisotopes and its precision and rapidity. Optimal conditions were established using the murine L929 and human ESH-5L cell lines as target cells for detecting lymphotoxins produced by human lymphocytes. The data indicate that the L929 cell line was 10–50-fold more sensitive than the ESH-5L line to the lytic activity of cytotoxins produced by human phytohemagglutinin-P-activated T lymphocytes, or the cytotoxins produced by peripheral blood lymphocytes stimulated with various tumor cell lines. This assay system was also useful in detecting antibodies capable of neutralizing lymphotoxin activity and thus should be a suitable method to aid in the molecular characterization of these lymphokines.     

Lymphocyte-mediated cytotoxicity in isoniazid-associated hepatitis.

The release of lymphotoxin (LT) from peripheral blood lymphocytes of patients with isoniazid (INH)-induced hepatitis was studied, using L929 fibroblast target cells, as was the cytotoxic effect of these lymphocytes on murine hepatoma cells (L1469) and L929 fibroblasts, using a 3H-proline cytotoxicity assay. Evidence for LT release was found in five out of six patients, following stimulation of the peripheral blood lymphocytes with INH or isonicotinic acid (INA) conjugated to human serum albumin. In the direct cytotoxicity assay, cytotoxic effects on the hepatoma cells were enhanced by preincubation of the target cells with INH in five out of six patients tested. Although specificity with regard to the drug was demonstrable, tissue specificity was less certain in that enhanced killing of the fibroblast cell line was also found to occur following preincubation of the L929 cells with INH.     

Human cervical carcinoma cell lines contain an antigen identical to the tumor-specific 75 kDa antigen of HeLa cells: detection by viral acquisition

Purified vesicular stomatitis virus grown in the human cervical carcinoma HeLa cell line, VSV(HeLa), contains a 75 kDa tumor-specific antigen, detectable by immunoblotting of electrophoretically separated proteins with rabbit antiserum made against whole HeLa cells. Nearly identical results were obtained with VSV grown in the tumorigenic human hybrid ESH-5L cells, but not with the matched non-tumorigenic ESH-5E cells. Growth of VSV in 4 other independently isolated human cervical carcinoma cell lines led to the concentration of the same 75 kDa tumor-specific antigen by VSV. Infection of 2 other human cervical carcinoma cell lines did not lead to the detection of this antigen. The expression of the tumor-specific antigen correlated directly with the amount of RNA expression from human papillomavirus integrated in the DNA of these cells, irrespective of whether the papillomavirus was type 16 or 18.     

鼠抗人OX40L功能性单克隆抗体的研制及其生物学特性的鉴定

目的　鼠抗人OX4 0L分子功能性单克隆抗体的研制及其生物学特性的鉴定。方法以高表达人OX4 0L分子的转基因细胞L92 9/OX4 0L为免疫原 ,常规免疫BALB/c小鼠 ,采用B淋巴细胞杂交瘤技术进行细胞融合 ,并以L92 9/OX4 0L为阳性抗体筛选细胞 ,L92 9/mock为阴性抗体筛选细胞 ,经免疫荧光标记和流式细胞术分析、反复筛选和多次克隆化培养 ,筛选出特异分泌鼠抗人OX4 0L分子单克隆抗体的杂交瘤细胞株 ;采用Westernblot、Ig亚型快速定性试纸法、间接免疫荧光法、竞争结合抑制试验和3 H TdR增殖试验等对单抗进行生物学特性的鉴定。结果　成功获得 3株持续、稳定分泌鼠抗人OX4 0L单克隆抗体的杂交瘤细胞株 ,命名为 9H10、4C12和 1G1。对单抗的生物学功能的研究结果表明 ,3株单抗均能识别活化B细胞和成熟DC表达的OX4 0L分子 ,且能抑制成熟DC对T细胞的促增殖作用 ,并与阻断型抗人B7 1单抗具有协同作用。结论　获得的 3株分泌鼠抗人OX4 0L功能性单克隆抗体的杂交瘤 ,所分泌的抗体具有特异性地识别人OX4 0L分子并能阻断OX4 0 /OX4 0L共刺激信号及抑制DC对T细胞的激发作用。     

人B-CAM/Lu基因逆转录病毒载体的构建及其在L929细胞中的表达

目的 克隆人B-CAM/Lu基因,构建其逆转录病毒表达载体,获得稳定高表达B-CAM/Lu的L929细胞株.方法 RT-PCR技术克隆人B-CAM/Lu基因,并插入逆转录病毒载体pEGZ中,该重组逆转录病毒载体与pH456、pH460两个辅助病毒载体一起,共转染包装细胞293T,并感染L929细胞,经Zeocin筛选获得的细胞株通过RT-PCR、Western blot及间接免疫荧光鉴定细胞中B-CAM/Lu基因mRNA的转录和蛋白表达.结果 成功获得人B-CAM/Lu基因,测序正确,亚克隆至逆转录病毒载体pEGZ后,经转染筛选,获得的抗性L929细胞株通过RT-PCR和Western blot分析,检测到B-CAM/Lu mRNA的转录和目的 蛋白的表达,通过间接免疫荧光确定该蛋白定位表达在L929转基因细胞膜上.结论 成功克隆并构建了人B-CAM/Lu基因的重组逆转录病毒表达载体,获得稳定高表达B-CAM/Lu蛋白的L929细胞株,为将其作为免疫源,制备B-CAM/Lu单抗用于镰刀型红细胞病及一些肿瘤疾病的检测诊断打下了基础.     

WEHI164－C1细胞株检测TNF的MTS／PMS比色法的建立

本文用有限稀释法对ＷＥＨＩ１６４细胞进行了亚克隆，从１２株中筛选出一株对ＴＮＦ高度敏感的亚克隆细胞株ＷＥＨＩ－Ｃｌ。ＭＴｓ的还原产物具有良好的水溶性，ＭＴＳ／ＰＭＳ比色法与ＭＴＴ法相比较具有简便、快速的优点。我们首先将ＭＴＳ引入细胞毒的检测，用ＷＥＨＩ１６４－Ｃｌ亚克隆株建立了检测ＴＮＦ的ＭＴＳ／ＰＭＳ比色法。此方法不仅简便、快速．而且敏感度高（比常规Ｌ９２９细胞检测法敏感１０～１５倍）、特异性强（ＩＬ－１、ＩＬ－２、ＩＬ－６、ＰＨＡ、ＣｏｎＡ、ＬＰＳ对检测结果均无明显影响）。     

Human T cells from autoimmune and normal individuals can produce tumor necrosis factor

T cell clones derived from patients with autoimmune diseases were found to be capable of producing tumor necrosis factor (TNF). This was demonstrated by stimulating the clones, in the absence of accessory cells, with antibodies against the Ti/T3 complex and with recombinant interleukin 2 (IL2). Analysis of RNA extracted from these clones showed that TNF mRNA was more abundant than lymphotoxin (LT) mRNA. We also found that TNF protein in the supernatants of these clones was generally more abundant than LT as assessed by using the murine L929 cell assay. TNF production was not limited to T cells from autoimmune individuals, since the T cell tumor HUT78 and T cells purified from the peripheral blood of healthy individuals also made TNF. Unlike the T cell clones, HUT78 produced greater amounts of LT mRNA than TNF mRNA. Induction of TNF mRNA in T cells from healthy individuals displayed a two-signal requirement (phorbol myristate 13-acetate and phytohemagglutinin or OKT3 and phorbol myristate 13-acetate), similar to that described for the induction of the T cell lymphokines IL 2 and interferon-gamma (IFN-gamma). Additionally we found that IL2 alone was sufficient to induce TNF in these cells when they had been precultured with phytohemagglutinin for 7 days to express IL 2 receptors. The cloned T cells we have characterized also produce IFN-gamma which was detected in the supernatants of the clones using a radioimmunoassay. The evidence suggests that T cells can produce TNF and have the potential to deliver by themselves the dual and synergistic signals of TNF/LT and IFN-gamma to target cells, a process which may be of importance in the pathogenesis of human autoimmunity.     

Correlation between killing activity towards the murine L929 cell line and expression of membrane-associated lymphotoxin-related molecule of human lymphokine-activated killer cells.

Human lymphokine-activated killer (LAK) cells expressed a membrane-associated lymphotoxin-related molecule (mLT) which was detected by flow cytometric analysis with anti-lymphotoxin antibody. Upon removal of exogenous interleukin-2 from LAK cell culture medium and another 24 h cultivation, the expression of mLT was decreased. Corresponding to the decrease of mLT expression, the killing activity of LAK cells towards L929 cells was remarkably reduced and killing of MIA PaCa-2 and U937 cells was moderately reduced, whereas killing of Daudi and K562 cells was fully restored. The supernatant of mLT-expressing LAK cells had no cytotoxic activity towards L929 cells in the absence of actinomycin D. Moreover, not only the killing of L929 cells but also that of human tumor cell lines (MIA PaCa-2, U937) by mLT-expressing LAK cells was partially inhibited in the presence of anti-lymphotoxin antibody. These results suggest an involvement of mLT in the killing of some tumor target cells by LAK cells.     

A sensitive method to measure PHA-induced cytotoxicity to adherent target cells using [3H]uridine as a terminal label

This paper describes a modification of the PHA-induced cytotoxicity test of human peripheral blood lymphocytes against a tumour-derived adherent cell line (HeLa), in which the surviving target cells are labelled with [³H]uridine at the end of the assay. There is a direct correlation between [³H]uridine incorporation and the number of adherent target cells. The test proves to be very sensitive at low effector: target cell ratios. Frozen stored cells can be used in this system, a particular advantage because of the possibility of increasing the reproducibility of the assay by using the same batch of cryopreserved lymphocytes as a reference standard in each experiment. PHA-induced cytotoxicity was mainly found in the T cell enriched fraction.     

一株鼠抗人BTLA功能性单克隆抗体的研制及其生物学特性鉴定

为了研制鼠抗人BTLA功能性单克隆抗体,以高表达人BTLA分子的基因转染细胞L929/BTLA为免疫原,常规免疫BALB/c小鼠,采用B淋巴细胞杂交瘤技术进行细胞融合,并以基因转染细胞293T/BTLA和293T/mock作为抗原,筛选阳性杂交瘤克隆,经间接免疫荧光标记和流式细胞术分析、反复鉴定和多次克隆化培养,筛选获得分泌特异性鼠抗人BTLA分子单克隆抗体的杂交瘤细胞株;采用Ig亚型快速定性试纸法、细胞核染色体计数、竞争结合抑制试验和T增殖抑制试验等对单抗进行生物学特性的鉴定。结果表明,成功获得一株持续、稳定分泌鼠抗人BTLA单克隆抗体的杂交瘤细胞株8H9,该单抗可特异性识别基因转染细胞以及静止与活化T淋巴细胞上表达的BTLA分子,单抗8H9和BTLA交联后能显著抑制鼠抗人CD3单抗对T细胞激发的增殖作用。     

Triggered human mucosal T cells release tumour necrosis factor-alpha and interferon-gamma which kill human colonic epithelial cells.

T cell activation can lead to local tissue injury in organ culture studies of human fetal jejunum, either directly through cytotoxicity or indirectly by the release of cytotoxic cytokines. The goal of this study was to establish in vitro whether cytotoxic cytokines can be released by isolated colonic T cells and what cytokine interactions are required for killing of human colonic epithelial cells. Cytokine-containing supernatants were induced by incubating unseparated lamina propria lymphocytes (LPL) or mucosal T cell subpopulations (separated by indirect panning) with anti-CD3 and/or K562 target cells for 18 h at 37 degrees C. Cytokines were measured by cytotoxicity assays using L929 (murine fibroblast) and HT-29 (human colonic tumour) lines as target cells in combination with blocking anti-cytokine antibodies. Supernatants derived from unseparated, CD4+ (greater than 95% pure) and CD8+ (greater than 90% pure) LPL were cytotoxic to L929 targets (350 U/ml, 230 U/ml and 100 U/ml tumour necrosis factor-alpha, respectively). All or nearly all of the cytotoxicity was due to the presence of tumour necrosis factor-alpha (little or no tumour necrosis factor-beta was detected). These same supernatants were cytotoxic (up to 32% lysis at 1/4 dilution) to HT-29 targets in a 48-h 111In release assay. Recombinant tumour necrosis factor-alpha and interferon-gamma alone produced minimal killing of HT-29, but together killed the HT-29 target cells. Anti-tumour necrosis factor-alpha or anti-interferon-gamma alone blocked killing of HT-29 target cells by LPL-derived supernatants, although anti-tumour necrosis factor-beta had no effect upon killing of HT-29. These results demonstrate that human LPL T cells, triggered by addition of anti-CD3 and target cells, produce tumour necrosis factor-alpha and interferon-gamma, both of which are required for optimal killing of HT-29. Simultaneous release of these cytokines in the vicinity of epithelial cells during immune responses could play an important role in the mucosal damage in chronic inflammatory states such as inflammatory bowel disease.     

Automated fluorometric assay for T cell cytotoxicity

A fluorometric assay avoiding the use of radioactivity has been developed for detecting cytotoxic T lymphocytes (Tc cells). The method involves labelling targets with Hoechst dye no. 33342 (H33342) which becomes brightly fluorescent on binding to DNA. Lysis of target cells by Tc cells is quantified by measuring the release of fluorescent H33342 into the supernatant of culture wells. The fluorescence is measured using an automated Microfluor reader which allows results to be obtained rapidly. The assay has been used to detect alloreactive Tc cells and H-2 restricted Tc cells against influenza virus in a short-term 6 h assay using P815 and L929 as targets with comparable results to those obtained with 51Cr labelling. In contrast, lymphocyte blasts were found to be less sensitive in 6 h fluorometric assays when compared with the 51Cr assay. In long-term overnight assays (possible because of the low spontaneous release of H33342 from targets) lymphocyte blasts gave high specific lysis and some anti-self reactivity. The cause of the anti-self reactivity may reflect fundamental differences between the H33342 and 51Cr release assays.     

一株识别肿瘤细胞上CD40突变体分子的单克隆抗体的研制及其生物学功能研究

目的:以本科室发现肿瘤细胞上表达的CD40 787AA突变为基础,研制识别肿瘤细胞上CD40突变体分子的单克隆抗体(mAb),并对其生物学特性作初步分析.方法:以转人CD40突变体转基因细胞L929-CD40mu为免疫原,免疫6～8周龄的雌性BALB/c小鼠;采用B淋巴细胞融合技术,将免疫小鼠脾脏细胞与Sp2/0融合,以L929-CD40mu转基因细胞为抗体筛选阳性细胞,免疫荧光标记法对杂交瘤进行反复筛选和多次的克隆化培养;采用快速定性试纸法及竞争抑制结合试验分析该mAb的亚类及抗原识别位点;免疫印迹法对该mAb进行鉴定;采用MTT法分析mAb在体外对肿瘤细胞的抑制增殖效应以及PI-annexin V方法进行细胞凋亡测定.结果:获得1株稳定分泌鼠抗人CD40mu mAb的杂交瘤细胞株(命名为10C5),该mAb能特异性地识别人肿瘤细胞株H08910表达的CD40突变体分子,而不识别正常扁桃体B淋巴细胞及血管内皮细胞表达的CD40分子,并且能够在体外促进肿瘤细胞凋亡.结论:成功地研制出1株特异性识别肿瘤细胞上CD40突变体分子的mAb,该mAb具有体外抑制肿瘤细胞生长并促进其凋亡的作用.     

A quantitative nitroblue tetrazolium assay for determining intracellular superoxide anion production in phagocytic cells

Conventionally, a semi-quantitative microscopic nitroblue tetrazolium (NBT) assay is used to determine the production of superoxide anion (O2(-)) in various phagocytic cells. This microscopic assay is conducted by counting the cells containing blue NBT formazan deposits, which are formed by reduction of the membrane permeable, water-soluble, yellow-colored, nitroblue tetrazolium (Y-NBT) by O2(-). However, this assay is semi-quantitative and is prone to observer bias. In the present study, we modified the NBT assay by dissolving the blue formazan particles using 2M potassium hydroxide and dimethylsulfoxide and then measured its absorbance using a microplate reader at 620nm. The absorbance of dissolved NBT increased in proportion to cell number (r = 0.9907), incubation time, and stimulus concentration. To test the usefulness of this modified assay, we compared the abilities of a number of types of phagocytic cells to produce O2(-). The cells examined included murine macrophage cell lines (RAW 264.7 and J774), freshly prepared murine peritoneal macrophages and neutrophils, a human myeloid cell line (PLB-985), and freshly prepared human peripheral blood neutrophils. In addition, we demonstrate that nitric oxide produced by RAW 264.7 cells does not interfere with the modified colorimetric NBT assay. Taken together, our results indicate that the modified colorimetric NBT assay is simple, sensitive, and quantitative, and that it can be used to determine the amounts of intracellular O2(-) produced by phagocytic cells. Thus, this assay is sensitive enough to measure, quantitatively, even the small amounts of O2(-) produced in monocytes and macrophages that are not detectable by the conventional microscopic NBT assay.     

Effects of iodinated fatty acid ester on human hepatocellular carcinoma cells.

The interaction between Lipiodol and cells was studied by treating Lipiodol in a human hepatocellular carcinoma cell line(Hep) and mouse fibroblast cell line (L929). Irregular, sustained radioactivity was released from both cell lines shortly after incubation in the radioiodinated Lipiodol mixed media. Lipiodol droplets were found to be firmly attached to the cells following the incubation and these cells were strongly positive for fat stains. The radioiodinated Lipiodol demonstrated the same behavior of accumulation within the cell and on the cell membrane. Although the amount of Lipiodol attached was almost equal in both of the cell lines, the final amount accumulated in the cells was larger in the Hep cells. The accumulation of Lipiodol within the cell and on the cell membrane may play a significant role for its selective targeting and its prolonged retention in the solid tumor.     

A specific and reliable bioassay for the detection of femtomolar levels of human and murine tumor necrosis factors

A reliable, highly sensitive, cytolytic bioassay for the quantitation of both human and murine tumor necrosis factor (TNF) is described. The assay is 2-180-fold more sensitive than other currently described bio- or immunoassays (limits of detection: 500 fg/ml (29 fmol/l) human TNF-alpha, 200 fg/ml (12 fmol/l) murine TNF-alpha and 130 fg/ml (7 fmol/l) human TNF-beta). The assay, which uses L929-8, a newly isolated subclone of the murine fibroblastoid cell line L929, detects human TNF-alpha approximately 180-fold more sensitively than previously described L929 subclone assays. Maximum sensitivity is obtained by preincubating L929-8 cells at 37 degrees C with 2 micrograms/ml actinomycin D (1-2 h), then culturing with TNF at 40 degrees C for 20 h in medium containing high serum (15% FBS). Relative viable cell content in 96-well microtiter plates is determined colorimetrically by uptake of the non-carcinogenic dye neutral red. Other cytokines have no effect, either alone or in combination with TNF. Cytokines tested were IL-1 through IL-6, GM-CSF, G-CSF, CSF-1, LIF, TGF-beta, NGF, Epo or IFN-gamma, LPS, PGE2, dexamethasone and cyclosporin A, also have no effect, either alone or in combination with TNF. L929-8 cells maintain the above sensitivity to TNF for at least 4 months in continuous culture. Thus, the assay allows rapid, inexpensive, reliable and specific quantitation of rodent and human TNFs. Its very high sensitivity should allow accurate detection of biologically active TNF in biological fluids such as human serum.     

一株鼠抗人PD-1功能性单克隆抗体的研制及其生物学特性的鉴定

研制特异性鼠抗人PD-1功能性单克隆抗体,并对其生物学特性进行鉴定。以高表达人PD-1分子的基因转染细胞L929/PD-1作为免疫原,常规免疫BALB/c小鼠,采用B淋巴细胞杂交瘤技术进行细胞融合,以L929/PD-1作为抗体筛选细胞,L929/mock为对照细胞,经间接免疫荧光标记和流式细胞术分析、反复筛选和多次克隆化培养,筛选出分泌特异性鼠抗人PD-1单克隆抗体的杂交瘤细胞株;采用Western blot、Ig亚型快速定性试纸法、间接免疫荧光法、竞争结合抑制试验和MTT增殖实验对单抗进行生物学特性的分析。结果表明,成功获得1株特异、稳定分泌鼠抗人PD-1单克隆抗体的杂交瘤细胞株,命名为6E2。对6E2生物学功能的研究结果提示,该单抗能够识别活化T细胞表达的PD-1分子,且在体外能够显著抑制T细胞的增殖和细胞因子的分泌。获得的特异性鼠抗人PD-1功能性单克隆抗体,通过激发PD-1负性途径能够有效抑制T细胞的功能,为进一步研究PD-1信号奠定了物质基础。     

A two-site sandwich immunoradiometric assay of human lymphotoxin with monoclonal antibodies and its applications

Three monoclonal antibodies (MoAbs L49-15, L81-11 and L238-14) were raised against recombinant human lymphotoxin (rLT) derived from E. coli containing the cDNA sequence specifying LT. MoAb L81-11 strongly neutralised the cytotoxicity of LT derived either from E. coli or the RPMI 1788 lymphoblastoid cell line, whilst the other two MoAbs were only weakly neutralising in this respect. L81-11 and L238-14 MoAbs bound to different antigenic determinants on the rLT molecule, but neither bound to other lymphokines such as the structurally related tumour necrosis factor (TNF). As such, these MoAbs were ideal reagents for immunoassay of LT and a very sensitive, highly specific immunoradiometric assay (IRMA) was developed. This assay was rapid to perform and was capable of detecting as little as 10 pg/ml of LT. Application of the LT IRMA in combination with previously developed human gamma-interferon (IFN-gamma) and human TNF-specific IRMA (Crane et al., 1985; Meager et al., 1987) permitted independent estimations of these three substances to be carried out in parallel. By these means, it was found that RPMI 1788 produced both LT and TNF, but not IFN-gamma. Extensive analyses on cytokine (monokine and lymphokine) preparations derived from a variety of activated lymphocytes are also reported. Co-production of LT, TNF and IFN-gamma was a common finding, even occurring in alloantigen-specific T helper cell clones.     

Differentiation Between Virulent and Avirulent Strains of Rickettsia prowazekii by Macrophage-Like Cell Lines

The growth of avirulent (E) and virulent (Breinl) strains of Rickettsia prowazekii was compared in four mouse macrophage-like cell lines (RAW264.7, J774.1, P388D1, and PU5), one human macrophage-like cell line (U937-1), and the mouse fibroblast line L929. The E and Breinl strains grew equally well in L929 cells. However, all of the mouse macrophage-like cell lines clearly differentiated between the two strains by restricting the growth of the E strain relative to that of the Breinl strain. A nonuniform response to infection was sometimes observed in which E strain rickettsiae were cleared from the majority of the infected cells, but multiplied in some of the remaining infected cells. The human line U937-1 was not very effective at differentiating the E and Breinl strains. Addition of rabbit antirickettsial antiserum to the Breinl or E strains of R. prowazekii immediately before infection of L929 cells caused a marked decrease in the initial infection but had no effect on the subsequent growth of the rickettsiae in the L929 cells. In contrast, addition of antiserum to Breinl or E strain rickettsiae immediately before infection of macrophage-like cell lines caused either no change or an increase in the initial infection. Most of the rickettsiae that infected the mouse macrophage-like cell lines in the presence of antiserum were destroyed in these cell lines. Thus, when the infection took place in the presence of antiserum, the mouse macrophage-like cell lines no longer differentiated between the E and Breinl strains. These data indicate that mouse macrophage-like cell lines should be a useful model system for defining the differences between the E and Breinl strains of Rickettsia prowazekii, differences which should lead to an understanding of the biochemical basis of virulence in this organism.     

In vitro quantitation of cell-mediated immunity in guinea-pigs by macrophage reduction of nitro-blue tetrazolium.

In the cell-mediated immune (CMI) system lymphocytes from sensitized animals incubated with antigen manufacture and release lymphokines which activate the hexose-monophosphate shunt in macrophages. The rate-limiting enzyme of this activation is NADPH oxidase, the activity of which can be quantitated by the amount of nitro-blue tetrazolium reduced to formazan, a blue precipitate. Data is presented which demonstrates that lymphokine-activated macrophages can be microscopically quantitated, both in the direct and indirect assays, by counting the number of macrophages containing formazan precipitate. The indirect component of this assay correlates directly to the skin test diameter. Further, it correlates better to the skin test than another assay for CMI, the macrophages aggregation factor assay. The simplicity and reproducibility of this assay provides another method whereby lymphokine activation of physiological events in macrophages can be determined.