Analysis of c-Ha-ras gene mutations in skin tumors induced in carcinogenesis-susceptible and carcinogenesis-resistant mice by different two-stage protocols or tumor promoter alone

In the present study we describe the molecular analysis of c-Ha-ras gene mutations in 47 papillomas and 17 carcinomas developed in two lines of mice, carcinogenesis-susceptible (Car-S) and carcinogenesis-resistant (Car-R), selectively bred for extreme susceptibility or resistance to chemical skin carcinogenesis initiated and promoted with different doses of 7,12-dimethylbenz[a]anthracene (DMBA) and 12-O-tetradecanoylphorbol-13-acetate (TPA). This study also presents the analysis of c-Ha-ras gene mutations in 22 papillomas and 22 carcinomas in Car-S mice initiated with DMBA and promoted with benzoyl peroxide (BzPo) and in seven papillomas and one carcinoma from a group of uniniated Car-S mice that received only BzPo treatment. The data showed that a A(182)-->T transversion in the c-Ha-ras gene was present in 100% and 81% of the skin tumors developed in Car-S and Car-R mice, respectively, after DMBA initiation and TPA promotion, suggesting that differences in genetic susceptibility can influence the frequency of c-Ha-ras mutations in the skin tumors produced. The same A(182)-->T mutation with an incidence of 68% was found in papillomas from DMBA-initiated and BzPo-promoted Car-S mice. The difference in the mutation frequency between DMBA/BzPo and DMBA/TPA papillomas suggested that the promotion step contributes to the final mutation pattern. The tumor induction experiment with BzPo alone showed that this compound can induce tumor development in 26% of Car-S mice, and the molecular analysis of the tumors showed a broad mutation spectrum, including mutations in codons 12, 13, and 61 of the c-Ha-ras gene. Mol. Carcinog. 30:111-118, 2001.

Genetics of chemical carcinogenesis: analysis of bidirectional selective breeding inducing maximal resistance or maximal susceptibility to 2-stage skin tumorigenesis in the mouse

We report on bidirectional selective breeding, initiated from a genetically defined foundation population and carried out to selection limit, for producing lines of mice endowed with maximal resistance (Car-R) or maximal susceptibility (Car-S) to 2-stage skin tumorigenesis. The initial population resulted from a balanced intercrossing of 8 inbred strains of mice. The tumors, induced by a single application of DMBA (initiation) and twice weekly applications of TPA (promotion), were benign papillomas; their number at the end of the promotion period was the phenotype chosen for assortative mating. Afterward, the majority of them regressed while others progressed to malignant carcinomas. The Car-R line was selected through a strong challenge, while the Car-S line selection was based on responses to decreasing concentrations of DMBA and TPA. The selection limit was reached after 14 or 15 generations showing progressive interline divergence, which strongly suggests the interaction of several quantitative trait loci (QTL). The phenotypic difference was extremely large: the tumor response was 73 times higher in Car-S than in Car-R mice, though the applied concentrations of DMBA and TPA were 100 and 40 times lower, respectively. The mean heritability realized during the selective breeding was 0.20 in Car-R and 0.49 in Car-S. Our results are compatible with a minimal QTL estimate of 8 in the Car-R line and of 9 or 10 in the Car-S line. The Car-S line is also much more susceptible to carcinoma induction. An association of coat color with tumorigenesis was observed in interline F2 segregants. The Car-R and Car-S lines, obtained through a long-lasting breeding program, are a unique model for identifying the QTL involved in chemical tumorigenesis and will be provided to interested investigators.

Skin tumorigenesis by initiators and promoters of different chemical structures in lines of mice selectively bred for resistance (Car-r) or susceptibility (Car-s) to two-stage skin carcinogenesis

Carcinogenesis-resistant (Car-R) and carcinogenesis-susceptible (Car-S) mice were obtained applying a bi-directional selective breeding approach to a two-stage skin carcinogenesis protocol, using 9,10-dimethyl-1,2-benzanthracene (DMBA) as initiator and 12-O-tetradecanoylphorbol-13-acetate (TPA) as promoter. Sixteen generations of selection produced a remarkable interline difference in responsiveness to two-stage skin carcinogenesis between Car-R and Car-S: identical DMBA (25 microgram) and TPA (5 microgram) doses induced papillomas in 100% of Car-S compared with 3.3% of Car-R mice and maximal responses of 14.3 or 0.03 papillomas/mouse, respectively, despite the shorter promotion applied to Car-S (49 vs. 208 days). To define the factors determining this great difference, Car-R and Car-S mice were challenged by initiators/promoters chemically unrelated to those used for selection. Both lines were subjected to either initiation by N-methyl-N-nitrosourea (MNU) followed by TPA promotion, or promotion by benzoyl peroxide, or 1,8-dihydroxy-3-methyl-9-anthrone (chrysarobin) following DMBA initiation. Initiation with MNU induced a 10-fold tumour incidence in Car-S compared with Car-R mice, and a 32-fold difference in tumour induction rate. The 2 lines also differed markedly in susceptibility to benzoyl peroxide promotion: Car-S mice initiated with 25 microgram DMBA and promoted with 7.5 mg benzoyl peroxide showed a 12-fold tumour incidence and a 103-fold tumour induction rate compared with the corresponding Car-R group. Both lines, however, were refractory to chrysarobin promotion. The progression of papillomas to carcinomas was examined in all Car-S groups. The incidence of mice that developed carcinomas was 57% in MNU-initiated mice. Benzoyl peroxide was also able to promote carcinoma development in Car-S mice, though with a lower incidence (30.4%) than TPA.

Low antibody responsiveness is found to be associated with resistance to chemical skin tumorigenesis in several lines of Biozzi mice

High and low antibody responder lines of mice from Selections I, III and G were assayed for two-step skin tumorigenesis using a protocol consisting in initiation with 7,12-dimethylbenz[a]anthracene (DMBA) and promotion with 12-O-tetradecanoylphorbol-13-acetate (TPA). Concordant results were obtained in the three selections: low antibody responder mice were shown to be significantly more resistant to tumor induction than the high responder counterparts. The difference was observed for all parameters: kinetics and percentages of tumor incidence and tumor multiplicity. The three bidirectional selective breeding experiments differed in several respects namely, the origin of the foundation populations, the antigens and immunization protocols used during the selection, as well as the breeding unit environments. Therefore, the consistent results relative to tumorigenesis strongly suggest that some of the alleles relevant to multispecific 'low' antibody production could contribute to the resistance to cutaneous chemical tumorigenesis.

Effect of genetic modification of acute inflammatory responsiveness on tumorigenesis in the mouse

Two distinct bidirectional selective breedings for quantitative traits were initiated from identical genetically heterogeneous mouse populations. The resulting lines are characterized by maximal or minimal acute inflammatory responsiveness (AIR): AIRmax and AIRmin lines, respectively, and by resistance or susceptibility to chemical skin tumorigenesis: Car-R and Car-S lines, respectively. The AIR response to s.c. injection of polyacrylamide microbeads, measured by cell content in the local exudate, was 10 times higher in AIRmax than in AIRmin mice. The response to selection was asymmetrical: the realized heritability was 0.26 in AIRmax and 0.008 in AIRmin, and resulted from the additive effect of 7-11 quantitative trait loci (QTL). Low responsiveness was globally dominant in F1 and 48% of F2 segregant variance was found to be due to genetic factors. These findings are the first demonstration of innate regulation of AIR by germ line genes. Susceptibility to skin tumorigenesis induced by a two-stage initiation (DMBA)-promotion (TPA) protocol was lower in AIRmax mice than in AIRmin mice, a 6-fold difference in tumor induction rate. Intense AIR was found to be associated with resistance, and low AIR with susceptibility to tumorigenesis, in F2 segregants chosen for extreme AIR phenotypes. At least some of the AIR QTLs therefore contain genes controlling tumorigenesis. Tumor phenotypes differed more in Car-R and Car-S than in AIRmax and AIRmin lines, indicating that QTLs unrelated to AIR, contribute to the host response to tumorigenesis. The extreme phenotypes/genotypes of the four selected lines and the known genetic constitution of their foundation population, offer new possibilities to discriminate the genes/mechanisms controlling two important traits: AIR and response to chemical tumorigenesis. Collaborative projects will be favorably considered. The description of tumor resistance genes in AIRmax and Car-R mice may be helpful for epidemiology and therapy of human cancer.

Genetic control of immune responsiveness, aging and tumor incidence

Age-related alterations of the immune system affect both antibody and cell-mediated immune responses, T-cell responses being more severely affected than B-cell responses. Within the T-cell population, aging leads to replacement of virgin by memory cells and to accumulation of cells with signal transduction defects. Changes in T-cell subsets and in cytokine production profiles may produce suitable conditions for T-cell-mediated disregulation of antibody responses characterized by the production of low affinity and self-reactive antibodies. Also B-cells exhibit intrinsic defects and natural killer (NK) cell activity a profound loss in old mice. Whether age-related immune disfunctions influence life span and tumor incidence has been examined in mice genetically selected for high or low antibody responsiveness. It has been found that genetic selection of vigorous antibody responses in most cases produces mice with longer life span and lower lymphoma incidence. Moreover, the results of genetic segregation experiments indicate that antibody responsiveness and life span are polygenic traits regulated by a small number of the same or closely linked loci. Mice genetically selected for high or low mitotic responsiveness to PHA exhibit low or high tumor incidence, respectively, but no difference in life span, suggesting that T-cell activity is restricted to immune surveillance of neoplastic transformation. Studies on mice genetically selected for resistance or sensitivity to chemical carcinogenesis have uncovered loci that control both resistance to tumor induction and longevity while have no effects on immunity and disease incidence. Thus, the relative role of the immune system in conditioning the duration and the biological quality of life remains to be determined.

Genetics of chemical carcinogenesis--III. Tissue-specificity of the genes controlling susceptibility and resistance to skin carcinogenesis in the mouse

Carcinogenesis-resistant (Car-R) and carcinogenesis-susceptible (Car-S) mice have been obtained by the method of bi-directional selective breeding. After 10 generations of selection Car-R and Car-S mice show a remarkable difference in their response to chemical carcinogenesis. Car-R and Car-S mice, initiated and promoted by skin application of 9,10-dimethyl-1,2-benzanthracene (DMBA) and 12-O-tetradecanoylphorbol-13-acetate (TPA) reach a tumour multiplicity of 0.05 and 6.2, respectively, after 49 days of promotion. When benzo[a]pyrene (B[a]P) is topically applied for initiation, followed by TPA promotion, Car-R and Car-S mice maintain a large difference in sensitivity to skin tumour induction. Car-S mice are also more susceptible than Car-R mice to complete carcinogenesis produced by single or repeated applications of DMBA only. On the contrary, when DMBA or B[a]P are administered by subcutaneous injection rather than by topical application, no significant difference in tumour incidence is observed between the two lines. All tumours induced by topical administration of carcinogens on the skin are of epithelial origin, whereas the tumours produced by subcutaneous injection are of connectival origin. These observations suggest a tissue-specific effect of the selected genes, probably restricted at the skin level.

Genetics of chemical carcinogenesis--II. Papilloma induction and malignant conversion in susceptible (Car-s) and resistant (Car-R) lines of mice produced by bidirectional selective breeding and in their (Car-S X Car-R) F1 hybrids

Susceptible (Car-S) and resistant (Car-R) lines of mice separated by 10 consecutive generations of bidirectional selective breeding present a very large difference in responsiveness to two-stage skin carcinogenesis. Car-S mice initiated with 0.5 micrograms 9,10-dimethyl-1,2-benzanthracene (DMBA) and promoted with 0.25 micrograms 12-O-tetradecanoyl-phorbol-13-acetate (TPA) for 77 days showed a papilloma incidence of 88% and a tumour multiplicity of 3.2 +/- 0.4 (mean +/- SE), with a tumour induction rate of 0.415. Car-R mice initiated with larger DMBA and TPA doses (50 micrograms and 20 micrograms respectively) and promoted for 111 days gave a comparable papilloma response: incidence 65%, tumour multiplicity 3.2 +/- 0.6 and tumour induction rate 0.288. The difference in papilloma response between the two lines is due to the interaction of genetic and environmental factors. In order to overcome the genetic effect with environmental factors and induce in Car-R a papilloma response comparable to that of Car-S, the DMBA dose had to be increased up to 100 times, that of TPA 40 times and the promotion time augmented by 44%. Papilloma to carcinoma conversion 112 days after the end of promotion depends on the DMBA and TPA doses applied. The number of carcinomas induced in Car-S mice and in (Car-S X Car-R) F1 hybrids was larger than that induced in Car-R mice, but the ratio of carcinoma conversion was lower, therefore a larger proportion of the small number of papillomas induced in the Car-R mice progressed to malignancy. The dominance effect measured in (Car-S X Car-R) F1 hybrids demonstrated that the susceptibility to papilloma induction was an incomplete dominant character (d/a = 0.38), whereas for carcinoma conversion the resistance was incompletely dominant (d/a = -0.49).

Comparison of 7,12-dimethylbenz(a)anthracene-DNA adduction in the epidermis of two lines of mice selected for resistance (CAR-R) or susceptibility (CAR-S) to skin carcinogenesis

Two lines of mice were produced by bidirectional selective breeding: one resistant (CAR-R) and one susceptible (CAR-S) to two-stage skin carcinogenesis by dimethylbenz(a)anthracene and 12-O-tetradecanoyl-phorbol-13-acetate. The dimethylbenz(a)anthracene-DNA adduct formation was compared in the two lines by a postlabeling procedure so as to determine whether the striking interline difference observed as to tumor incidence could (in part) be due to differences in the formation of DNA-reactive metabolites. Results show that qualitatively, adduct profiles in CAR-R and CAR-S epidermis are similar. Quantitatively, the total binding level is slightly higher in CAR-S versus CAR-R mice during the 30-day follow-up. However, these minor differences do not increase in function of the response to selection observed through three consecutive generations. A 2- or 4-week promotion with 12-O-tetradecanoylphorbol-13-acetate enhances the decrease of adduct level in the two lines. This effect is somewhat more pronounced in CAR-S mice. Results strongly suggest that the expression of the genes responsible for CAR-R/CAR-S phenotypic difference affects mainly the postinitiation stages.

Genetics of chemical carcinogenesis. 1. Bidirectional selective breeding of susceptible and resistant lines of mice to two-stage skin carcinogenesis

Six generations of a bidirectional selective breeding model for producing lines of mice susceptible (Car-S) and resistant (Car-R) to two-stage skin carcinogenesis are described. Initiation was with 9,10-dimethyl-1,2-benzanthracene (DMBA single application), and promotion with 12-O-tetradecanoyl-phorbol-13-acetate (TPA twice weekly). The selective breeding was initiated with a highly genetically polymorph foundation population, produced by the intercrossing of eight inbred mouse strains. The Car-S line was produced by assortative mating of the mice presenting the largest number of tumors induced by low DMBA and TPA doses, the Car-R line by mating tumorless mice or mice showing the smallest number of tumors induced by large DMBA and TPA doses. The character investigated was expressed as per cent tumor incidence and as tumor multiplicity per mouse. The mean heritability of the susceptibility character for the two first generations was 0.84 for tumor incidence and 1.3 for tumor multiplicity; these values decreased to 0.53 and 0.44 respectively for the two consecutive generations. The heritability of the resistance character maintained a constant value of 0.29 +/- 0.04 for tumor incidence, and 0.53 +/- 0.08 for tumor multiplicity. The progressive response to selection indicates that the characters investigated are subject to polygenic regulation, even though some genes may have a major effect on the susceptibility character. The interline separation in F5, challenged with the same initiation and promotion schedule, is very large. In the Car-S line, tumor incidence was 82.5% and tumor multiplicity 4.9/mouse on promotion day 49, whereas the corresponding values for the Car-R line were 4.5% and 0.1/mouse on promotion day 81.

Inheritance of immune responsiveness, life span, and disease incidence in interline crosses of mice selected for high or low multispecific antibody production

High (H) and low (L) antibody responder lines of mice separated by selective breeding present a maximal interline difference in antibody (Ab) response to Ag of different specificities (general genetic regulation). The analysis of SRBC agglutinin response in H line, L line, F1 hybrids, F2, and backcross segregants demonstrates that Ab responsiveness is a polygenic trait regulated by the additive interaction of 5 to 7 independent loci, with an incomplete dominance (44% +/- 7%) of the high response character, and a 30% +/- 10% impact of the environmental factors. The life span of H, L, F1, F2, and backcross populations is correlated positively with 2-ME-resistant agglutinin response (r = 0.97, p less than 0.001) and negatively with 2-ME-sensitive agglutinin response (r = 0.95, p = 0.01) (interpopulation correlation). Similar correlations are also observed in individuals of the various populations, especially in F1 x L backcross, in which the largest phenotypic variance is found. The positive correlation between Ab responsiveness and life span was confirmed by ELISA titration for distinct IgG isotypes (intrapopulation correlation). Malignant lymphomas and chronic nephritis were the two most common diseases observed. The age-adjusted incidence of such diseases, which is largely affected by environmental factors, accounts for the longer life span of H, as compared with L, mouse populations. The longevity of the 30% or less survivors, chiefly determined by the rate of physiologic aging, is a polygenic character regulated by the cumulative interaction of 3 to 7 independent loci, with a complete dominance of the long life trait and an impact of the environmental factors of about 60%. Thus we have grounds for regarding general Ab responsiveness and life span as polygenic traits regulated by a small number of identical or closely linked gene loci, and immune responsiveness as a defense mechanism against neoplastic and inflammatory diseases.

Inheritance of immune responsiveness, life span, and disease incidence in interline crosses of mice selected for high or low multispecific antibody production

High (H) and low (L) antibody responder lines of mice separated by selective breeding present a maximal interline difference in antibody (Ab) response to Ag of different specificities (general genetic regulation). The analysis of SRBC agglutinin response in H line, L line, F1 hybrids, F2, and backcross segregants demonstrates that Ab responsiveness is a polygenic trait regulated by the additive interaction of 5 to 7 independent loci, with an incomplete dominance (44% +/- 7%) of the high response character, and a 30% +/- 10% impact of the environmental factors. The life span of H, L, F1, F2, and backcross populations is correlated positively with 2-ME-resistant agglutinin response (r = 0.97, p less than 0.001) and negatively with 2-ME-sensitive agglutinin response (r = 0.95, p = 0.01) (interpopulation correlation). Similar correlations are also observed in individuals of the various populations, especially in F1 x L backcross, in which the largest phenotypic variance is found. The positive correlation between Ab responsiveness and life span was confirmed by ELISA titration for distinct IgG isotypes (intrapopulation correlation). Malignant lymphomas and chronic nephritis were the two most common diseases observed. The age-adjusted incidence of such diseases, which is largely affected by environmental factors, accounts for the longer life span of H, as compared with L, mouse populations. The longevity of the 30% or less survivors, chiefly determined by the rate of physiologic aging, is a polygenic character regulated by the cumulative interaction of 3 to 7 independent loci, with a complete dominance of the long life trait and an impact of the environmental factors of about 60%. Thus we have grounds for regarding general Ab responsiveness and life span as polygenic traits regulated by a small number of identical or closely linked gene loci, and immune responsiveness as a defense mechanism against neoplastic and inflammatory diseases.

Polygenic control of quantitative antibody responsiveness: restrictions of the multispecific effect related to the selection antigen

Among the differences observed between the various high (H) and low (L) antibody responder lines of mice resulting from distinct bidirectional selective breedings, one of the most puzzling is the variation in the "multispecific effect," i.e., in the modification of antibody responses to antigens unrelated to those used during the selection. The best examples are the H and L lines of selection IV, selected on the basis of responses to somatic antigen of Salmonella which do not differ in their antibody responses to sheep erythrocytes (SE). However, a wide range of variability is observed in the responses of (HIV X LIV)F2 hybrids to this antigen, and it was therefore hypothesized that distinct groups of genes might regulate antibody responses to SE and the somatic antigen. Indeed, a new selection (IV-A) for anti-SE responsiveness started from these (HIV X LIV)F2 successfully produced a high and a low anti-SE responder line. The results of selection IV-A and the variance analysis of (HIV-A X LIV-A)F2 hybrids are reported. They are roughly similar to those in selection I, also carried out for anti-SE responsiveness. In vivo attempts to identify the major regulatory mechanism which contributes to the interline difference indicate that the efficiency of macrophage accessory function has been modified in selection IV-A, as was observed in selection I, whereas this function did not differ in HIV and LIV lines. Probably in relation to the involvement of macrophage function there is a notable increase of the multispecific effect in selection IV-A when compared with selection IV. The results of selection IV-A demonstrate that responsiveness to heterologous erythrocytes and to somatic antigen of Salmonella are under separate polygenic control operating through distinct regulatory mechanisms. The choice of the selection antigen and immunization procedure is of major importance for defining the gene interaction operating in each selective breeding experiment and the extent of its multispecific effect.

Genetic regulation of the specific and non-specific component of immunity

Bi-directional selective breeding for antibody (Ab) responsiveness to heterologous erythrocytes (Selection I) produced a high (H) and a low (L) responder line of mice which were also remarkably separated for Ab responses to many unrelated natural antigens (Ags) such as heterologous proteins, viruses, bacteria, parasites and haptens carried by these immunogens. The character "quantitative Ab responsiveness" is controlled by several independently segregating loci (polygenic regulation). The major genetic modification is produced at the level of macrophage activities. The Ag is slowly catabolized and persists for a long time on the macrophage membrane of the H line, whereas it is rapidly destroyed in L line macrophages. The bactericidal and bacteriostatic activity of the macrophage is also strong in the L line and weak in the H line. The opposite genetic regulation of Ab responsiveness and macrophage activity is a fundamental phenomenon for understanding natural and vaccination-induced anti-infectious immunity. The L line is more resistant than the H line against the infections due to intracellular microorganisms (Salmonellae, Yersinia, Mycobacteria, Brucellae, Leishmania) where the macrophage plays the dominant defensive barrier. The H line is more resistant than the L line to the extracellular microorganisms which are efficiently counteracted by a strong antibody response (Pneumococcus, Klebsiella, Plasmodia, Trypanosoma). The intensity of T cell-mediated immunity as measured by delayed type hypersensitivity, which is independent of the genetic regulation of antibody responsiveness, is correlated with the degree of nonspecific inflammation produced at the site of the reaction by the Ag injection in non-sensitized mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of silica on the genetic regulation of antibody responsiveness

The high (H) and low (L) antibody responder lines of mice produced by selective breeding are characterized by different modifications in immunocompetent cell potentialities, according to the immunization procedure used for the selection process. In selections I and II, the difference in antibody responsiveness between H and L lines was clearly shown to depend mainly on macrophage function: the more rapid catabolism of antigens in L mice was the main cause of the low antibody production. In contrast, up to now, no difference has been observed between H and L mice of selections III and IV in terms of the macrophage accessory role. The administration of silica particles has a well known impairment effect on macrophage activity. Therefore, the effect of silica injection on the kinetics of antibody responses to selection antigens was compared in H and L mice of the four selections. Silica was given either intravenously or locally in one hind footpad 6 or 24 h before immunization by the same route. Silica treatment consistently improved antibody responsiveness in the L mice of selections I and II, but had no effect in the L mice of selections III and IV. The antibody responses of the H lines of the four selections were not substantially modified by silica injections. Therefore, the silica treatment reduced the interline difference in antibody responses in selections I and II only, by interfering with the expression of the genetic modification of macrophage activity. However, a similar effect was not obtained with other substances known to affect macrophages, including dextran sulphate or carrageenan. The results reported here are in agreement with the above-mentioned statement that the genetic modification of macrophage function plays a major role in the interline difference in selections I and II and is not involved in selections III and IV.

Effect of genetic modification of antibody responsiveness on resistance to Toxoplasma gondii infection

Resistance to Toxoplasma gondii infection was studied in the high (H/f) and low (L/f) antibody responder lines of mice that were selected on the basis of quantitative antibody responsiveness to the flagellar antigen of Salmonella (selection III). No interline difference was observed in resistance to a highly virulent strain of T. gondii. In contrast, H/f mice were much more resistant than L/f mice to a moderately virulent strain of T. gondii: a 5000-fold difference in terms of the 50% lethal dose was found. The degree of resistance in (H/f X L/f)F1 hybrids was intermediate compared with that in parental lines for both mortality and survival time. The antibody titers to Toxoplasma antigens measured during the course of the infection were significantly higher in H/f than in L/f mice. This interline difference was underestimated because parasite multiplication occurs faster in L/f mice, which increases antigenic stimulation. The stronger resistance of H/f mice is probably due to their higher capacity of antibody production in the course of infection.

Regulatory function of Thy-1-negative cells: V. A lymphokine of B cell origin (BEF) induces in vitro high antibody response in genetically selected low responder mice

Studies were conducted on two lines of mice genetically selected, respectively, for high (AB/H) and low (AB/L) antibody production, in order to identify the mechanism by which genes involved in the selection express their functions. It was found that B cell-derived enhancing factor (BEF), a lymphokine of B cell origin which acts on T cells by preventing the activation of suppressor cells, is effective in inducing high responses in low responder mice, whereas it is ineffective in modulating antibody production in high responder mice. As a result, no difference was found between the responses of AB/H and AB/L mice when spleen cells were stimulated in vitro in the presence of BEF. AB/H and AB/L mice do not seem to differ in their B cell functions since no difference was found in the capacity of B cells of either line to synthesize antibodies in the presence of T cell-replacing factor (TRF), or to produce endogenous BEF. These data indicate that, at least in vitro, the character of general responsiveness of these two mouse lines mainly reflects differential reactivity of T suppressor cells. Since the two lines represent, respectively, the maximal and minimal responsiveness of an outbred population of animals, it is suggested that the individual difference in antibody response is related to individual differences of T suppressor cells in responding to the immunogen.

Basal immunoglobulin serum concentration and isotype distribution in relation to the polygenic control of antibody responsiveness in mice

Serum Ig concentration and isotype distribution were determined in the high (H) and low (L) responder lines selected for antibody response to complex immunogens. Data were recorded in normal and postimmunization sera from the H and L lines produced by five independent selective breedings (selections I, II, III, IV, and V). Ig levels were much higher in H than in L mice of all the selections. In four selections this interline difference increased further after immunization with the selection antigens. This is in agreement with the general effect of the polygenic control of antibody responses operating in H and L lines. The Ig isotype profiles of normal sera were different in each line; however, similitudes were noticed between H and L lines in selections I and II. In contrast, in selections III, IV, and V a similar interline difference was observed: the lack of IgG2a isotype in L lines only. After immunization there were minor alterations of the isotype profiles except in the H lines of selections III and IV, in which a clear inverse modification of IgG1 and IgG2a proportions occurred. The characteristic pattern of each selection may be partially dependent on isotype-restricted regulatory effects in relation to the immunization procedure used for selective breeding.

Resistance of high and low antibody responder lines of mice to the growth of avirulent (BCG) and virulent (H37Rv) strains of mycobacteria

The resistance to Mycobacterium bovis (BCG) of lines of mice selected for high (H) or low (L) antibody responsiveness was estimated from the rate of BCG multiplication in the organs. During the first 2 weeks after i.v. infection with 5 X 10(6) CFU, BCG multiplied faster in the spleens of H than of L mice. Afterwards there was a more drastic reduction of viable BCG counts in H mice than in L mice so that the residual BCG counts were significantly lower in H mice than in L mice, not only in the spleen but also in the liver and lungs. On the 14th day of infection, the spleen and liver enlargement and the increase of phagocytic activity were similar in the two lines, suggesting an identical T lymphokine release. In contrast with BCG, during the first 2 weeks after infection with 7 X 10(5) CFU, M. tuberculosis (H37Rv) multiplied in the spleens of L mice at a similar or a slightly faster rate than in the spleens of H mice. On the 4th week, the viable H37Rv counts were reduced in H mice whereas L mice did not survive the infection. In mice vaccinated with BCG 5 months before virulent challenge, the multiplication of H37Rv was inhibited in the H and L lines. The protective effect of BCG is therefore stronger in L mice taking into account their higher innate susceptibility to H37Rv. This might be due to the higher level of living BCG found in L mice at the time of challenge.

Genetic selection for antibody responsiveness in mice: further evidence for inverse modification of macrophage catabolic activity without alteration of the expression of T-cell-mediated immunity

Five selective breedings have been performed for the character "antibody production" in mice. Two of them, Selection I and Selection II, carried out for maximal (H) and minimal (L) antibody response to heterologous erythrocytes, gave similar results concerning the genetic parameters and the extent of modification of antibody response to unrelated antigens (non-specific effect of the selection). Macrophage characteristics and the expression of T-mediated immunity were investigated in H and L mice of Selection II and compared with results already obtained in Selection I. The phagocytic activity of macrophages was similar in the two lines, whereas an important interline difference was observed concerning the persistence of the immunogen, which was much shorter in L than in H mice. The more rapid antigen catabolism in L mice explains why the threshold immunogenic dose was higher in these mice and why the antibody response was much more improved in L than in H mice by repeated antigen administration. Results on skin allograft rejection, delayed-type hypersensitivity and responsiveness to T mitogen demonstrated that H and L mice have a similar ability to mount T-mediated immunity reactions. Two findings obtained in Selection I were therefore confirmed: 1) macrophage catabolic activity is modified by selection in the opposite direction of antibody production: low antibody responsiveness is associated with high macrophage activity and vice-versa; 2) and the expression of cell-mediated immunity and of the humoral immune response are at least partially under independent genetic regulation.

Isotype IgE class-specific suppression in the Biozzi 'High' and 'Low' lines of mice

The suppression of the production of IgE antibody was investigated with the Biozzi 'High' and 'Low' lines of mice. Using the adoptive transfer method formerly experimented with SJL mice (donor I immunized with 0.2 microgram dinitrophenylated ovalbumin, donor II hyperimmunized with 10 micrograms keyhole limpet hemocyanin and donor III being unimmunized mice) IgE suppression was observed in recipients irradiated with 600 R only with the 'Low' line.

Inheritance of post-vaccinal resistance against Plasmodium berghei infection in mice

The protective effect of specific vaccination against Plasmodium berghei (P. berghei) was compared in terms of survival percentage in DBA/2, C3H, outbred albino mice and in two lines of mice produced by selective breeding for either high or low antibody responsiveness to sheep erythrocyte (H and L lines respectively). The efficacy of induced protection varies according to genetic constitution. It is very strong in H line and albino mice, intermediate in DBA/2 and very weak in L line and C3H. The inheritance of post-vaccinal resistance to infection was studied in F1 hybrids and backcrosses between C3H and the other lines. The control was polygenic in all cases. The dominance of the characteristic depends on the strain combination. On the whole the results suggest the non-identity of the genes controlling protection in the various lines. The lack of a quantitative parameter for a more precise genetic analysis of protective immunity in inbred lines is stressed, since both anti-P. berghei antibody production and parasitaemia proved to be unreliable.

[Plasmodium berghei: antibody response and protective immunity induced by vaccination]

The authors have studied the behaviour of Swiss mice and of 5 inbred strains of mice in order to investigate: the protective effect, in the homologous infection test, of six vaccine inoculations of irradiated parasites belonging to two strains of Plasmodium berghei: ISTISAN and K173; the capacity to produce humoral antibodies after vaccine treatments and during infection; the probable correlation between the high antibody titre and the protection against infection. The results of the present study show that the antibody response plays a precise role in the immunity induced by vaccination. There is a certain degree of correlation, which is more evident for K173 vaccine, between the level of antibody response during infection and the protective efficacy of vaccination.

Quantitative effect of H-2-linked gene(s) on antibody response to human gamma-globulin

H-2-linked gene(s) have been found to play a role in the quantitative regulation of response to human gamma-globulin (HGG) in mice selected for high or low antibody responsiveness to sheep erythrocytes. Unexpectedly, in a random genetically heterogeneous population of F2 interline hybrids, the gene(s) linked to the H-2 phenotype of H mice has a "low" effect, and the gene(s) linked to the H-2 phenotype of L mice a "high" effect on the magnitude of antibody response to HGG. In H and L mice, the non-specific polygenic control of antibody responsiveness is able to compensate/counteract the inverse effect of HGG-specific H-2-linked gene(s) since the usual interline difference is observed.

Genetic parameters of the polygenic regulation of antibody responsiveness to flagellar and somatic antigens of salmonellae

Selective breedings of mice were carried out for quantitative antibody responsiveness to flagellar Ag., f (Selection III) or somatic Ag., s (Selection IV) of two non cross-reacting Salmonellae (Salm. tm., Salm. or.) alternated for immunization of consecutive generations. At the selection limit, these selections produced homozygous high (H) and low (L) responder lines for the character investigated: peak agglutinin response to optimal secondary immunization. The responsiveness to both f and s Ags. is submitted to polygenic regulation. The heritability (h2) realized during the selective breeding was 0.37 +/- 0.07 for the response to fAg. and 0.40 +/- 0.1 for the response to s Ag. The respective part of genetic and environmental variance in F2 hybrids was 64% and 36% in selection III and 61% and 39% in selection IV. In the two selections, the dominance variance is negligible (less than 1%), therefore the genetic variance is essentially additive. The additive variance calculated as the heritable fraction of the F2 hybrid variance is somewhat lower, the reason for this difference is discussed. The quantitative antibody response to f Ag. in selection III is controlled by about seven independent loci. The antibody response to s Ag. in selection IV is controlled by about four independent loci. A possible association of relevant genes with the H-2 locus was investigated. In selection III, no significant participation if H-2 linked genes, in the regulation of responses to f and s Ags. of Salm. tm and Salm. or. could be demonstrated. In selection IV a partial contribution of H-2 linked genes was observed concerning responsiveness to both f and s Ags. of Salm. tm. but not Salm. or. Ags. The H-2 effect accounts for 25% of the total interline difference.

Evidence for distinct polygenic regulation of antibody responses to some unrelated antigens in lines of mice selected for high or low antibody responses to somatic antigen of Salmonella

The effect of the selective breeding of mice for high or low antibody production to complex immunogens is largely "nonspecific", since it modifies the responsiveness of high (H) and low (L) lines to many antigens unrelated to the selection antigen. However, the nonspecific effect of the polygenic control operating in these lines is not a general feature. For example, the group of genes in selection IV, carried out for responsiveness to somatic antigen of Salmonella, does not modify the responses to sheep erythrocytes (SE). Despite equivalent responses in H and L mice of selection IV, a large variability was found in individual responses of F2 interline hybrids, which demonstrates the presence of alleles with high or low effect on responses to SE. A selective breeding (Selection IV-A) was therefore initiated from this F2 population for responsiveness to SE.A progressive interline divergence occurred during the first seven generations of selection; the interline separation was due to polygenic regulation (about four independent loci from a preliminary estimate). Equivalent responses to the s antigen of Salmonella are observed in the two lines. This constitutes additional evidence for distinct polygenic regulation of responses to SE and to somatic antigen. Moreover, the pattern of responses to several unrelated antigens (nonspecific effect) also differs between Selections IV and IV-A.

[Effect of the age of the mouse on the action of Corynebacterium parvum in inhibiting the growth of 2 syngenetic tumors]

The antitumor properties of Corynebacterium parvum have been studied in Mice of different ages of two inbred strains: XVII Mice and C3H Mice grafted with syngeneic tumors. The antitumor protection was very weak in young Mice: no effect on mortality rate, only an increase in mean survival time was observed. The highest level of protection was obtained in 2-5 month old Mice (100% of survival) In aged Mice this antitumor protection decreases more rapidly in C3H Mice than in XVII Mice. It is interesting to note that 21 day old XVII Mice and 25 day old C3H Mice, non weaned, are partially protected by C. parvum (50% survival), while treated Mice of the same age, already weaned, are not.

[Passive transfer of "Corynebacterium parvum" anti-tumour protection by stimulated peritoneal cells ]

A partial anti-tumour protection can be induced by transfer of peritoneal cells from mice pretreated with Corynebacterium parvum, in the two experimental tumours studied: a mammary carcinoma syngeneic to C3H mice and a lymphosarcoma syngeneic to XVII mice. This protection is abolished by heating the peritoneal cells at 70 degrees C for 30 min, by a 2,200-rad irradiation or by a non-lethal irradiation of the recipient mice. Transfer of normal peritoneal cells did not produce any anti-tumour protection in C3H mice but induced the same effect as stimulated cells in XVII mice. The difference in these results could be explained by the routes of injection of peritoneal and tumour cells: intraperitoneally in C3H mice and intravenously in XVII mice. It cannot be excluded that the protective effect induced by the injection of the stimulated peritoneal cells could be produced by the anti-tumour activity of the transferred C. parvum phagocytized by these cells.

[Effect of silica on the anti-tumour activity of "Corynebacterium parvum" (author's transl)]

Silica, a specifically toxic substance for macrophages, has been used to study the role of these cells in the Corynebacterium parvum-induced anti-tumour protection. In the two experimental tumours studied, silica, C. parvum and tumour cells were injected by the same route: the intravenous route in the case of lymphosarcoma in XVII mice and the intraperitoneal in that of mammary carcinoma in C3H mice. The inhibition of the anti-tumour effect of C. parvum by the administration of silica was more pronounced in C3H than in XVII mice. Silica administration has only a weak and transient depressive effect on the stimulation of macrophage phagocytic activity induced by C. parvum. In addition, silica injection increased the adjuvant effect of C. parvum on the sheep red blood cell antibody response. These results suggest that the silica induced abrogation of the anti-tumour effect of C. parvum could be due to a local inhibition of macrophage stimulation at the tumour inoculation site.

Differences in the genetic control of primary and secondary antibody responses

Primary and secondary antibody responses to f and s antigens of Salmonella typhimurium have been studied in H and L lines of mice genetically selected for primary reponse to sheep erythrocytes (SE) (Selection I). The range of interline separation obtained (non-specific effect of Selection I) was as large as for the selection antigen in the primary response to f antigen and slightly smaller in the primary response to s antigen. For these two antigens the interline difference was reduced after booster. The kinetics of responses were compared with those obtained in H and L lines of Selections III and IV carried out for secondary responses to f and s antigens of S. typhimurium respectively (specific effect of Selection III and IV). The genetic analysis was made in Selection I from the variances of individual agglutinin titres obtained in large groups of interline hybrids immunized with S. typhimurium. These calculations gave a reliable estimate of the effective number of independent loci regulating primary and secondary responses. The results demonstrated a major difference in the genetic control: a single locus regulated the secondary response to f antigen while six loci were involved in the control of the primary response. A similar difference was evident for s antigen. The primary response was likely to be under polygenic regulation although the effective number of loci could not be calculated, while the secondary response was under monogenic control.

Correlation between genetic regulation of antibody responsiveness and protective immunity induced by Plasmodium berghei vaccination

High (H) and low (L) antibody responder lines of mice were produced by two independent bidirectional selective breedings for quantitative antibody responsiveness to heterologous erythrocytes (selection I and selection II). In both selections the antibody response to P. berghei antigens was 8- to 10-fold higher in H than in L lines. The character "high response" presents an incomplete dominance o- 18% in selection I and 67% in selection II. In selection II the variance analysis indicates that at least three independent loci intervene in the regulation of responsiveness to P. berghei antigens. The innate resistance and the protective efficacy of vaccination against P. berghei infection induced by parasitized erythrocytes was measured in H and L lines and in the interline hybrids F1, BcH, and BcL of selections I and II. No very significant difference was observed in the innate resistance to P. berghei infection between H and L mice of both selections. Vaccination induced a very efficient protection in the two H lines (94 and 95% survival), whereas only a weak protection was induced in the two L lines (16 and 31% survival); the degree of protection is intermediate in interline hybrids F1, BcH, and BcL. In both selections a good linear correlation was demonstrated between the level of vaccination-induced antibody and the degree of resistance measured as percentage of survival. The present results indicate that the vaccination-induced P. berghei immunity is essentially due to the antibody response, whereas the bactericidal activity of macrophages and the cell-mediated immunity do not play a determinant role.

Deficiency of high-affinity anti-beta-D-galactosidase antibodies in selected low immune responder mice

Amount and affinity of anti-beta-D-galactosidase-activating antibodies (AAb) were studied in two lines of mice obtained by selective breeding for antibody response to heterologous erythrocytes. These lines, referred to as high (H) and low (L) lines, differ also in their responses to many antigens. Concerning AAb amounts, the maximal titer in H mice is higher than in L mice. However, the AAb levels in H mice decreased with increasing immunizing doses and became lower than in L mice for the highest dose. This fact can be explained in terms of intramolecular competition or suppression. Whereas the usual maturation pattern was observed in H mice, no AAb of high affinity were found in L mice, even after a minimal immunizing dose. At any dose tested, no maturation of AAb occurred until three months after immunization. This deficiency may be ascribed to B lymphocyte or macrophage modifications. A correlation between the deficiency of high-affinity AAb in L mice and their genetically induced low antibody responsiveness cannot be proved.

Genetic analysis of antibody responsiveness to sheep erythrocytes in crosses between lines of mice selected for high or low antibody synthesis

Two selective breedings of mice for minimal or maximal agglutinin response to heterologous erythrocytes were carried out (selection I and II). Preliminary reported data indicated that for both selections the heritability was between 0.18 and 0.36 and the number of relevant loci from 7--13. The results reported in this article are definitive since the data of ten to twenty generations at selection limit are available and large populations of interline hybrids F1, F2 and both backcrosses were analysed. The character 'high response' was partially dominant in F1 hybrids of both selections, the degree of this incomplete dominance was 0.27 in selection I and 0.54 in selection II. In selection I, 38% of the F2 variance was due to genetic factors (VG) and 62% to environmental effects (VE). The partition of phenotypic variance of F2 and backcrosses into additive variance (VA) and dominance variance (VD) was made according to three methods and the mean results were: VA = 0.72 and VD = 0.05. The resulting mean heritability was 0.35 and the number of relevant loci about ten. In selection II, 69% of the F2 variance was due to VG and 31% to VE. The three methods of variance calculation give somewhat discordant results. According to the more probable estimation (see discussion) VA = 0.95, the mean heritability was 0.23 and the number of loci, about 6. The results obtained in crosses between homologous lines of the two selections indicate that the two 'high' lines have probably identical homogeneous genetic constitution while the two 'low' lines contain some different 'high' effect loci.

In vitro immune response of spleen cells from mice genetically selected for high or low antibody production

The aim of this study was the identification of the cell type in which genes selected for high or low response to SRBC express their functions. Spleen cells from high (H) and low (L) responder mice were immunized with SRBC in the Mishell and Dutton system. An antibody response of different magnitude was found in cultures of H and L spleen cells, the difference being at least as great as that observed in vivo. This finding under experimental conditions allowing the exclusion of any influence of the animal milieu during the immune response, suggest macrophages, B, and T lymphocytes as possible target cells of gene action. In vitro cell separation and recombination experiments in which spleen cells were immunized with SRBC, TNP-LPS, or TNP-HRBC indicate that the genetic differences between H and L responders brought about by selective breeding are expressed in lymphocytes to greater extent than in macrophages. The role of histoincompatibility in the recombination experiments in unlikely but cannot be excluded. Among lymphocytes, B cells but not helper T cells were found more responsive in cultures of spleen cells from H than from L mice.

Mechanism of Corynebacterium Parvum anti-tumour activity. II. Protective effect in T-cell-deprived mice

The natural resistance to syngeneic mammary carcinoma was reduced by thymectomy alone in adult C3H mice or in mice thymectomized, lethally irradiated and restored with bone-marrow cells (Tx RB). The protective effect of C. parvum was not modified by adult thymectomy but it was reduced in Tx RB mice. The injection of thymic cells to Tx RB mice or the elimination of T cell precursors in bone-marrow cells injected in Tx RB mice did not increase the protective effect of C. parvum. These results were compatible with the hypothesis that T cells do not intervene in the mechanism of C. parvum protective effect.

Nonspecific genetic regulation of antibody responsiveness in the mouse

Four lines of mice were produced by selective breeding for quantitative agglutinin responsiveness to flagellar (f) or somatic (s) antigens (Ags) of Salmonellae: high (H) or low (L) responder lines to fAg and H and L responder lines to sAg. The Salmonellae contained both f and sAgs, the Ag used to perform the selection was the Selection Ag and the other was the Associated Ag. The selective breeding produced a progressive interline separation with an equivalent effect for both Ags. After 15 generations (F15) the level of agglutinin response was about 60 times higher in H than in L responders. About 50% of the phenotypic variation of the character investigated is determined by a group of immune response genes, the rest is due to environmental factors. The nonspecific effect of this group of immune response genes was investigated by measuring the responses to three independent antigens: Sheep erythrocytes (SE), dinitrophenyl-conjugated human IgG (DNP-HGG) and bovine IgG (BGG). The selection for fAg response produced an equivalent modification in the respnsiveness to the Associated Ag (97%) and to BGG (130%). This nonspecific effect was smaller for responsiveness to SE and DNP-HGG, 58% and 41% of the Selection Ag response, respectively. The selection for sAg response produced a nonspecific modification of responsiveness of 94% for the Associated Ag of 74% for BGG and 63% for DNP-HGG. An important exception concerned SE to which an equal antibody response is produced in high and low lines of sAg selection.

IgA antibody response to intragastric immunization in high and low immune responder lines of mice

Two lines of mice selected for genes controlling the character "quantitative agglutinin production" to heterologous erythrocytes were immunized orally by the intragastric administration of sheep red blood cells (SRBC). The quantity of circulating IgA anti-SRBC and the numbers of splenic plaque-forming cells of IgA and IgM classes were related to the genetic status of the animal lines.

[Non-specific polygenic regulation of antibody synthesis]

Four two-way genetic selections of outbred mice for the quantitative character "agglutinin production" to heterologous erythrocytes and flagellar or somatic antigens of Salmonella are briefly described. The principal genetic parameters regulating the quantitative antibody response are the following: 1) the character is polygenic; the number of independent loci is estimated between 7 and 16; 2) the heritability of the character (h2) is comprised between 0.17 and 0.21; 3) the maximal interline separation RT (4.8-7.8 log2) is reached after about 15 consecutive generations of selective breeding; (4) the rate of interline separation/generation RG is 0.32-0.48 log2. 5) The phenotypic variance V(P) of the foundation populations is due for 52%-63% to genetic factors V(G) and for 37%-48% to environmental factors V(E); 6) The effect of the selective breeding is essentially non-specific; it modifies the antibody responsiveness to many unrelated complex immunogens.

[Genetic analysis of the synthesis of IgE and hemagglutinating antibodies in high and low responder lines (HL and LL) of mice and their hybrids]

Immune responses depend upon the dose of antigen and the line of mice. Threshold doses of antigen are lower in HL, higher in LL and intermediate in hybrids. The responses obtained in F1, F2 and backcrosses demonstrate the genetic control of the interline difference. The correlation between IgE and hemagglutinating antibodies responses suggests a common genetic control for the synthesis of the two types of antibodies.

[Antitumor effect of Corynebacterium parvum]

The protective effect produced by pre-treatment with C. parvum is studied in two syngeneic tumours: mammary carcinoma in C3H mice and lymphosarcoma in XVII mice. The best anti-tumour effect is obtained when both C. parvum and tumour cells are injected by the same route, which, however varies for the two tumours. The study of the recovery of C. parvum protective effect after its suppression by a sub-letal dose of x-irradiation shows that, in the C3H mice, it is parallel to the restoration of the antibody response. On the contrary, in XVII mice, the recovery of the protection is obtained in mice still immunologically suppressed.

Study of the mechanism of Corynebacterium parvum anti-tumour activity. I. Protective effect on the growth of two syngeneic tumours

The protective effect of C. parvum against two different tumours - a lymphosarcoma and a mammary carcinoma - has been demonstrated. In the case of lymphosarcoma, a significant protective effect was obtained when both C. parvum and tumor cells were injected IV. In contrast in C3H mice the best protection was obtained when both C. parvum and mammary carcinoma cells were injected IP. Thus both C. parvum and tumour cells must be inoculated by the same route which, however, varies for different tumours. A very small dose of C. parvum still inhibited the growth of the two tumours. Splenectomy performed before C. parvum treatment did not interfere with the anti-tumour activity of C. parvum on the tumours. However, when splenectomy was performed after C. parvum injection, the protective ffect of C. parvum still persisted against XVII lymphosarcoma but not against C3H carcinoma.