Imbalanced MHC class II molecule expression at surface of murine B cell lymphomas.

To study the role of class II MHC expression in mouse lymphomagenesis, we examined the cell surface expression of I-A/E antigens on 24 spontaneous or murine leukemia virus (MuLV)-induced mouse B10.A (I-Ak, I-Ek) B cell lymphomas. Two primary B10.A B cell lymphomas were observed with strong I-Ek expression but with only minimal cell surface I-Ak expression. Both tumors are readily transplantable in syngeneic mice, with maintenance of their I-A-, I-E+ phenotype. Strikingly, one I-A-, I-E+ B cell lymphoma contains a (11; 17) translocation with a breakpoint on chromosome 17 that is localized within or very close to the H-2 complex. DNA of both tumors contains normal restriction enzyme fragments of the A alpha and A beta genes. Northern blot analyses indicated that one I-A-, I-E+ tumor strongly expressed A alpha, E alpha, and E beta mRNAs but possessed only a weak expression of A beta mRNA. The other B cell lymphoma showed A beta, E alpha, and E beta mRNA expression but only minimal A alpha mRNA expression. In 11 primary B10.A B cell lymphomas with a normal I-A+, I-E+ phenotype, no imbalances in A alpha/A beta mRNA levels were observed. The implications of these findings for the role of class II MHC expression in mouse B cell lymphoma-genesis are discussed.

Naturally occurring leukemia viruses in H-2 congenic C57BL mice. I. High lymphoma incidence following milk-borne transmission of virus.

Two modes of transmission of ecotropic type C viruses occur naturally in C57BL mice: maternal (i.e., through milk) and genetic. By selection of virus-positive and virus-negative B10.ASgSn [B10.A (H-2a)] mothers and foster-nursing of C57BL/10ScSn [B10 (H-2b)] newborns, four sublines of C57BL mice were obtained: B10.A V+, B10.A V-, B10 V+, and B10 V-. (V+ denotes positive for milk-transmitted B-tropic virus; V- denotes negative for milk-transmitted B-tropic virus). Milk transmission of naturally prevalent B-tropic virus (V+ sublines) led to persistent infection of all offspring over at least 8 generations. Milk transmission of virus was associated with a very high incidence of lymphomas. The H-2 complex influenced the titers of virus after milk transmission, which were higher in B10.A V+ mice than in B10 V+ mice. H-2 control of virus titers, as measured by serum p30 assay, was confirmed in (B10.A V+ X B10 V+)F2 mice. Resistance to the virus was dominant, because serum p30 levels in F1 and H-2a/b F2 animals were similar to those in the B10 V+ subline and lower than those in the B10.A V+ subline. The H-2 complex also influenced the incidence of lymphomas (78 and 42%, respectively, in the B10.A V+ and B10 V+ sublines). Most B10.A V+ lymphomas were of T-cell origin, whereas most B10 V+ lymphomas were classified as non-T/non-B cells. Genetic transmission of virus (V- sublines) led to heterogeneous expression of both N- and B-tropic viruses, which thereby established the mottled trait for expression of genetically transmitted type C viruses in C57BL mice. Genetic transmission was associated with a low incidence of lymphomas that occurred in senescence.

HIV-1 biological phenotype in long-term infected individuals evaluated with an MT-2 cocultivation assay.

OBJECTIVE: We have previously demonstrated that detection of syncytium-inducing (SI) HIV-1 in asymptomatic seropositive individuals is associated with rapid progression to AIDS. In the present study, we sought to develop and evaluate an HIV-1 phenotyping assay for the screening of large numbers of individuals. METHODS: Efficiency of HIV-1 isolation from patient peripheral blood mononuclear cells (PBMC) was studied with donor PBMC or seven different CD4+ T-cell lines as target cells. The biological phenotype of sequential isolates from 20 long-term asymptomatic HIV-1-seropositive individuals was determined by two different assays. RESULTS: Non-SI isolates, efficiently recovered by cocultivation with donor PBMC, were never isolated with T-cell lines as target cells. Direct cocultivation with MT-2 cells, but not with six other CD4+ T-cells, resulted in the efficient recovery of SI isolates. HIV-1 MT-2 tropism and SI capacity were shown to be coupled properties at the clonal level. SI isolates emerged in 10 out of 20 longitudinally-studied individuals. In these long-term infected individuals, appearance of SI isolates was associated with progression to AIDS. CONCLUSIONS: Direct cocultivation of patient PBMC with the MT-2 cell line is a sensitive, specific and convenient method to detect SI isolates. The availability of an assay suitable for the screening of large groups allows further study of the value of HIV-1 biological phenotyping as a prognostic marker.

Immunological and virological markers in individuals progressing from seroconversion to AIDS.

Six men were selected from a large cohort of homosexual men participating in a study on HIV infection that was followed from seroconversion to AIDS. The patients were studied retrospectively for immunological functions of T cells, T-cell subset distribution and biological phenotype of HIV. A severe decrease in anti-CD3 monoclonal antibody (MAb)-induced T-cell proliferation at seroconversion was observed in two out of six men. After this acute phase, CD4+ T-cell numbers were in the normal range in the early asymptomatic period; the proliferative response was subnormal, whereas the capacity to generate cytotoxic T cells (CTL) was normal. From seroconversion on, CD4+CD29+ memory T-cell numbers were decreased to approximately 50% of normal values, which may contribute to loss of T-cell reactivity. In the asymptomatic phase only slow-replicating non-syncytium-inducing HIV variants were observed. The T-cell proliferative response further declined with the depletion of naive CD4+ CD45RA+ T cells and CD4+ T-cell numbers started to decline. This second decrease in T-cell function coincided with the emergence of more rapidly replicating, often (four out of six) syncytium-inducing variants. At diagnosis of AIDS, T-cell proliferation and CD4+ T-cell numbers were extremely low in five out of six patients and CTL function had declined in three out of five individuals tested. Circulating CD8+ cells had gradually shifted to an immature CD38+CD28- phenotype. Our findings support the theory that HIV-induced immune dysfunction allows for the emergence of virulent HIV variants associated with CD4+ cell loss and disease.

Differential tropism of clinical HIV-1 isolates for primary monocytes and promonocytic cell lines.

Previously we demonstrated a correlation between a nonsyncytium-inducing (NSI), non-T-cell line tropic phenotype of HIV-1 isolates and the capacity to replicate in primary monocyte-derived macrophages (MDM). Here we demonstrate that these NSI, monocytotropic HIV-1 isolates lack the capacity to replicate in two promonocytic cell-lines, HL60 and U937. In contrast, most syncytium-inducing (SI) HIV-1 isolates with tropism for T-cell lines and generally non-monocytotropic were able to establish a productive infection in promonocytic cell lines. Similar differences in tropism for monocytes and promonocytic cell lines were observed with infectious molecular clones. Our results indicate that virological studies on promonocytic cell lines do not necessarily pertain to the HIV-1 infection of monocytes in vivo.

Genetic and functional analysis of a set of HIV-1 envelope genes obtained from biological clones with varying syncytium-inducing capacities.

To study HIV-1 envelope-mediated syncytium formation we have amplified, cloned, expressed, and sequenced individual envelope genes from a set of eight biological HIV-1 clones. These clones were obtained from two patients and display either a syncytium-inducing (SI) or nonsyncytium-inducing (NSI) phenotype. Upon expression through recombinant vaccinia virus, individual envelope gene products display heterogeneous syncytium-inducing capacities which reflect the phenotype of the parental biological HIV-1 clones in all cases. For the eight biological HIV-1 clones presented here, variation of the envelope gene alone is sufficient to explain the observed variable syncytium-inducing capacity of the respective parental viruses. In addition we determined the complete nucleotide sequence of these envelope genes. The predicted amino acid sequence revealed a considerable amount of variation located mainly in the previously denominated variable regions. In various regions of envelope genes obtained from the same patient, phenotype associated amino acid variation was found. This phenotype associated amino acid variation however, is not conserved between the two sets of envelope genes derived from different patients. Four envelope sequences derived from clones obtained from one patient showed phenotype-associated amino acid variation in the fusion domain. Sequencing of 12 additional fusion domains revealed that this same variation is found in four additional clones. However, a functional test performed on recombinant vaccinia expressing mutant envelope genes showed that this observed fusion domain variation does not contribute to the variation in syncytium-inducing capacity of the envelope gene product.

Ecotropic and dualtropic mink cell focus-inducing murine leukemia viruses can induce a wide spectrum of H-2 controlled lymphoma types.

Neonatal infection of C57BL and BALB/c mice by cloned ecotropic and dualtropic mink cell focus-inducing (MCF) murine leukemia viruses (MuLV) induces a wide spectrum of different lymphomas of T, B, and non-T/non-B cell types. Oncogenic dualtropic MCF viruses and poorly oncogenic ecotropic MuLV act synergistically in lymphomagenesis. Within one mouse strain virus-induced T-cell lymphomas arise earlier than B-cell lymphomas after neonatal inoculation of a single-cloned MuLV. The host genetic constitution, notably the H-2 complex has a marked influence on lymphoma type. This H-2 influence can be explained by an H-2-linked difference in penetration of the thymus early in life by oncogenic thymotropic MuLV, which in turn is correlated with, but not necessarily due to the magnitude of the anti-MuLV antibody response.

Antibody-dependent lymphocytotoxicity: an analysis of effector cell-target cell interactions.

Antibody-dependent lymphocytotoxicity (ADL) was studied with human peripheral blood lymphocytes as effector cells and P815 mouse mastocytoma cells, sensitized with rabbit IgG antibodies, as target cells. Enzyme-substrate-like kinetics were used to describe ADL inhibition induced by two types of inhibitors. Human IgG, both native and heat-aggregated, proved to be a competitive inhibitor of ADL at the target cell level. Human peripheral blood monocytes inhibited ADL in an apparently irreversible fashion, without appreciable evidence for competition. The data obtained provide strong support for the validity of an enzyme-substrate-like mechanism of ADL. Moreover, our results indicate that in order to measure the lytic capacity properly, cell populations, well defined as to their composition, should be used. In the second part of the study, it was investigated whether the two types of cells capable of lysing sensitized target cells, i.e., null cells and T cells, differed with respect to their affinity for the target cells. Application of enzyme-like kinetics revealed considerable differences in maximal killing rate between the two subsets of K cells. However, the parameter related to the affinity toward the target cells was found to be of the same magnitude for the two types of effector cells.

Decreased accessory cell function by human monocytic cells after infection with HIV.

We studied the effect of HIV infection on the human monocytic cell line U937. The cell line was infected with cellfree HIV, strain HTLV-IIIB. After 3 wk, a high reverse transcriptase activity was continuously detected in the supernatant of the cell line. Neither cytopathic effects nor changes in cell growth were observed. After infection, accessory cell function on T cell proliferation induced by anti-CD3 mAb of both IgG1 and IgG2a subclasses and Con A was tested. Accessory cell function provided by U937 cells started to decline 3 wk after inoculation with HIV. This correlated with detectable reverse transcriptase activity. The remaining accessory cell capacity varied between 10 and 60% of accessory cell function mediated by noninfected U937 cells. It was excluded that decreased FcR expression on U937/HIV cells contributed to the accessory cell defect in the anti-CD3-driven system. IL-2R expression on T cells, cocultivated with U937/HIV and anti-CD3, was minimal. The accessory cell defect could only be partly overcome by addition of rIL-2 or IL-1. Addition of high titer (10(4) TCID50) HIV or U937/HIV cells did not affect T cell proliferation, which rules out that the observed inhibition is caused by HIV infection of T cells or suppressive effects of U937/HIV cells. These results suggest that infection of APC may contribute to the induction of immunologic abnormalities in early HIV infection. Thus, monocytes/macrophages may not only serve as a reservoir for the dissemination of HIV, but may be an important target cell through which the immune system is affected.

Major histocompatibility complex class II-regulated immunity to murine leukemia virus protects against early T- but not late B-cell lymphomas.

We studied the relative importance of class I and class II major histocompatibility complex (MHC) immunoregulation in the control of T- and B-cell lymphomas induced by murine leukemia virus. Previously, we have described a mink cell focus-inducing (MCF) murine leukemia virus, MCF 1233, which induces not only lymphoblastic T-cell lymphomas but also follicle center cell or lymphoblastic B-cell lymphomas. We now report that the outcome of neonatal infection with MCF 1233 in H-2-congenic C57BL/10 and C57BL/6 mice is decisively influenced by the H-2 I-A locus. A total of 64% of H-2 I-Ak, d mice [B10.BR, B10.D2, B10.A(2R), B10.A(4R), and B10.MBR] developed T-cell lymphomas after MCF 1233 infection (mean latency, 37 weeks). In contrast, H-2 I-Ab [B10, B10.A(5R), B6], H-2 I-Ab/k [(B10.A x B10)F1 and (B10 x B10.A)F1], and H-2 I-Abm12 (bm12) mice were resistant against T-cell lymphomagenesis, but 65% of these H-2 I-Ab, b/k, bm12 animals developed B-cell lymphomas (mean latency, 71 weeks). Animals of T-cell lymphoma-susceptible strains that escaped from T-cell lymphomagenesis developed B-cell lymphomas with similar frequency as animals of T-cell lymphoma-resistant strains, but with a shorter latency. H-2 class II-determined regulation of antiviral immunity was reflected in the presence of high titers of antiviral envelope antibodies in T-cell lymphoma-resistant B-cell lymphoma-susceptible H-2 I-Ab, b/k, bm12 mice, whereas in T-cell lymphoma-susceptible H-2 I-Ak,d mice no antiviral antibodies were found. At week 4 after neonatal MCF 1233 infection, a high percentage of thymocytes were virally infected in both T-cell lymphoma-susceptible and -resistant mice. However, T-cell lymphoma-resistant animals cleared the thymic infection between weeks 4 and 10 of age, coinciding with a sharp rise in serum levels of antiviral antibodies. We conclude that the pleiotropic effects of MCF 1233 infection in H-2-congenic mice result from MHC class II I-A-determined T-cell response differences.

H-2 control of the cytotoxic antibody response against a newly defined MuLV-related cell-surface antigen: G(B10.A).

H-2-congeneic C57BL mice with milk transmission of B-tropic murine leukemia virus (V+ mice) have a much higher lymphoma incidence than the same strains without milk-transmitted virus (V- mice). Gene(s) within the major histocompatibility complex (H-2) influence virus titers, lymphoma incidence, lymphoma type and the anti-MuLV envelope antibody response. In this paper, we report that the prevalence of cytotoxic antibodies to virus-induced lymphomas is also regulated by the H-2 complex. Milk transmission of MuLV resulted in the formation of cytotoxic antibodies against primary virus-induced C57BL lymphomas. These antibodies detect an antigen that is also present on the RADAI tumor-cell line, and on normal spleen cells of young adult B10.A (H-2a) mice of both V+ and V- sublines, but not on spleen cells of young adult B10 (H-2a) mice of either subline. These cytotoxic antibodies were detected in the sera of B10V+ and B10.A(5R)V+ animals, but not in the sera of B10.AV+ mice. This indicates that the prevalence of these antibodies is controlled by a gene in the K- and/or I-A region of the H-2 complex. The presence of these cytotoxic antibodies in serum is recessively inherited. The specificity of the cytotoxic antibodies was investigated with a standard panel of transplantable tumor-cell lines. Of these, only the RADAI cells expressed the target antigen in direct cytotoxicity tests and by absorption. The ability of B10V+ sera to lyse the B10.AV+ and RADAI tumor cells is ascribed to antibody activity against a new MuLV-related cell-surface protein: G(B10.A). Immunochemical analysis and absorption experiments with different types of purified MuLV and MuLV-infected cell lines indicate that the cytotoxic antibodies belong to low-avidity IgM antibodies that are directed to MuLV.

Monocytotropic human immunodeficiency virus type 1 (HIV-1) variants detectable in all stages of HIV-1 infection lack T-cell line tropism and syncytium-inducing ability in primary T-cell culture.

We previously demonstrated a correlation between the presence of syncytium-inducing (SI) human immunodeficiency virus type 1 (HIV-1) variants showing tropism for cell line H9 and the occurrence of rapid CD4 cell decline and progression to AIDS. In contrast, in stable asymptomatic individuals, we detected only isolates with low replication rates that were non-syncytium-inducing (NSI) and nontropic for the H9 cell line. Here, we investigated the monocytotropism of established HIV-1 isolates with a panel of isolates and with biological HIV-1 clones with distinct phenotypes. Moreover, the prevalence and biological phenotypes of monocytotropic HIV-1 variants in the course of HIV-1 infection were analyzed in comparative primary isolation studies on peripheral blood lymphocytes (PBL) and monocyte-derived macrophages (MDM). In cell-free infection studies with MDM from eight blood donors, 13 of 17 NSI isolates but only 4 of 14 SI isolates were able to infect MDM. NSI isolates also infected significantly more different donors than SI variants (median, 3 of 8 versus 0 of 8). This enhanced monocytotropism of NSI isolates was confirmed in experiments with biological HIV-1 clones with distinct phenotypes recovered from the same donor. To investigate the prevalence and biological phenotypes of monocytotropic variants in different stages of HIV-1 infection, sequential isolates from peripheral blood mononuclear cell samples from nine asymptomatic individuals, five of whom progressed to AIDS and seven of whom had a known time of seroconversion, were recovered by cocultivation with both PBL and MDM. Monocytotropic variants were obtained from 37 of 42 time points. All monocytotropic variants were NSI in PBL culture and non-T-cell-line tropic, even when SI, T-cell-line-tropic HIV-1 variants could be recovered from the same patient sample by cocultivation with PBL. We conclude that monocytotropic HIV-1 variants mostly have an NSI phenotype in PBL and, in contrast to SI variants, are present at all stages of HIV-1 infection. These results suggest an important role for monocytotropic variants in the persistence of HIV-1 infection.

Tumor progression in murine leukemia virus-induced T-cell lymphomas: monitoring clonal selections with viral and cellular probes.

Clonal selections occurring during the progression of Moloney murine leukemia virus (MuLV)-induced T-cell lymphomas in mice were examined in primary and transplanted tumors by monitoring various molecular markers: proviral integration patterns, MuLV insertions near c-myc and pim-1, and rearrangements of the immunoglobulin heavy chain and beta-chain T-cell receptor genes. The results were as follows. Moloney MuLV frequently induced oligoclonal tumors with proviral insertions near c-myc or pim-1 in the independent clones. Moloney MuLV acted as a highly efficient insertional mutagen, able to activate different (putative) oncogenes in one cell lineage. Clonal selections during tumor progression were frequently marked by the acquisition of new proviral integrations. Independent tumor cell clones exhibited a homing preference upon transplantation in syngeneic hosts and were differently affected by the route of transplantation.

Relation between changes in cellular load, evolution of viral phenotype, and the clonal composition of virus populations in the course of human immunodeficiency virus type 1 infection.

The relationship between the evolution of human immunodeficiency virus type 1 (HIV-1) biologic phenotype, changes in the proportion of infected peripheral blood mononuclear cells, and the relative contribution of non-syncytium-inducing (NSI) and syncytium-inducing (SI) HIV-1 variants to virus load was studied during the course of HIV-1 infection. In 65 HIV-1-infected subjects, the proportion of infected CD4 T cells was higher in persons who carried SI variants. Longitudinal studies revealed that the emergence of SI HIV-1 variants can occur at relatively low numbers of HIV-1-infected cells. Emergence of SI variants frequently coincided with an increase of virus load due to an expansion of both NSI and SI variants, although the contribution of SI viruses to the total virus population significantly increased with time after SI phenotype conversion. These data indicate that NSI to SI phenotype conversion, rather than resulting from high virus load, is part of the sequence of events that leads to increased virus load and CD4 cell depletion.

Differential syncytium-inducing capacity of human immunodeficiency virus isolates: frequent detection of syncytium-inducing isolates in patients with acquired immunodeficiency syndrome (AIDS) and AIDS-related complex.

Human immunodeficiency virus isolates were studied with respect to syncytium-inducing capacity, replicative properties, and host range. Five of 10 isolates from patients with acquired immunodeficiency syndrome (AIDS) and AIDS-related complex were able to induce syncytia in cultures of peripheral blood mononuclear cells (MNC). In contrast, only 2 of 12 isolates from asymptomatic individuals had syncytium-inducing capacity. Syncytium-inducing isolates were reproducibly obtained from the same MNC sample in over 90% of the cases, independent of the donor MNC used for propagation. Syncytium-inducing capacity was shown to be a stable property of an isolate, independent of viral replication rates. Evidence was obtained that the high replication rate of syncytium-inducing isolates observed during primary isolation may be due to higher infectivity of these isolates. The finding that only syncytium-inducing isolates could be transmitted to the H9 cell line is compatible with this higher infectivity. The frequent isolation of syncytium-inducing isolates from individuals with AIDS-related complex or AIDS and the apparent higher in vitro infectivity of these isolates suggest that syncytium-inducing isolates may unfavorably influence the course of human immunodeficiency virus infection.

Evidence for a role of virulent human immunodeficiency virus (HIV) variants in the pathogenesis of acquired immunodeficiency syndrome: studies on sequential HIV isolates.

Sequential human immunodeficiency virus (HIV) isolates, recovered from a panel of longitudinally collected peripheral blood mononuclear cells obtained from 20 initially asymptomatic HIV-seropositive homosexual men, were studied for differences in replication rate, syncytium-inducing capacity, and host range. Eleven individuals remained asymptomatic; nine progressed to acquired immunodeficiency syndrome (AIDS) or AIDS-related complex (ARC) at the time point at which the last HIV isolate was obtained. In 16 individuals, only non-syncytium-inducing (NSI) isolates, with a host range restricted to mononuclear cells, were observed. From four individuals, high-replicating, syncytium-inducing (SI) isolates that could be transmitted to the H9, RC2A, and U937 cell lines were recovered. From two of these four individuals, SI isolates were obtained throughout the observation period. In the two others, a transition from NSI to SI HIV isolates was observed during the period of study. Three of these four individuals developed ARC or AIDS 9 to 15 months after the first isolation of an SI isolate. With the exception of the two individuals in whom a transition from NSI to SI isolates was observed, within a given individual the replication rate of sequential HIV isolates was constant. A significant correlation was found between the mean replication rate of isolates obtained from an individual and the rate of CD4+ cell decrease observed in this individual. In individuals with low-replicating HIV isolates, no significant CD4+ cell loss was observed. In contrast, recovery of high-replicating isolates, in particular when these were SI isolates, was associated with rapid decline of CD4+ cell numbers and development of ARC or AIDS. These findings indicate that variability in the biological properties of HIV isolates is one of the factors influencing the course of HIV infection.

Zidovudine sensitivity of human immunodeficiency viruses from high-risk, symptom-free individuals during therapy.

Human immunodeficiency type 1 isolates from 18 initially symptom-free men who were treated with zidovudine for 2 years were investigated for drug sensitivity. At the start all the men had persistent core antigenaemia; the acquired immunodeficiency syndrome developed in 6 during the study. The polymerase chain reaction was used to detect mutations at residue 215 of reverse transcriptase, a mutation associated with reduced drug sensitivity. After 2 years 16/18 isolates were mutant. However, after about 6 months of treatment the mutation was detected in only 7 isolates, 4 from individuals who subsequently had AIDS. Limited direct virus sensitivity data correlated with the genetic data. The rate of appearance of the 215 mutation seemed to correlate with CD4 counts and viral virulence.

Confirmation of HIV seropositivity: comparison of a novel radioimmunoprecipitation assay to immunoblotting and virus culture.

A recently developed radioimmunoprecipitation assay, using 125I-labeled human immunodeficiency virus (HIV) viral proteins enriched for glycoproteins gp120env, gp41env (GRIPA), was compared to the immunoblot assay with respect to sensitivity and specificity for the detection of antibodies to HIV. Longitudinal sets of serum samples of seroconverting homosexual men were studied, as were sera of six blood-bank donors likely to be false-positive in immunoblot. In addition, HIV isolation was attempted from white blood cells of these blood-bank donors and of seropositive and seronegative individuals. In sets of seroconversion samples, the GRIPA appeared at least as sensitive as the immunoblot. Some sera already were clearly positive in the GRIPA at a time when there was only weak reactivity in immunoblot. In contrast, sera from blood-bank donors that were regarded as false-positive in immunoblot were negative in GRIPA. Virus culture from these donors was also negative. It is concluded that reactivity in immunoblot to core proteins only may well be false-positive, whereas antibody reactivity in the radioimmunoprecipitation assay to p24gag solely suggests ongoing seroconversion. This feature, in addition to a sensitivity for anti-gp120env comparable to immunoblotting, makes the GRIPA a useful confirmatory assay in sera that yield conflicting results in other HIV-antibody assays.

Naturally occurring leukemia viruses in H-2 congenic C57BL mice. III. Characterization of C-type viruses isolated from lymphomas induced by milk transmission of B-ecotropic virus.

The prevalence of different host-range classes of murine leukemia virus (MuLV) was studied in C57BL mice with (V+) and without (V-) milk transmission of a naturally occurring B-tropic ecotropic MuLV. Virus isolates were studied with respect to growth properties, XC-plaque formation, antigen profiles of their envelope proteins (gp70 and P15(E)), gp70 tryptic-peptide maps, and their potential to induce lymphomas after inoculation into newborn mice. B-tropic ecotropic MuLV with the capacity to cause plaques in XC cells was isolated from almost all lymphomas of both V+ and V- sublines. The reaction patterns of these ecotropic isolates with monoclonal antibodies reactive with MuLV-env proteins and the tryptic-peptide maps of the gp70 molecule indicate that they are similar to each other and differ only slightly from the ecotropic MuLV in the spleens of young V+ animals, which is identical to the milk-transmitted virus. XC-, B-tropic dualtropic mink cell focus-inducing (MCF) viruses were isolated from the majority of different types of lymphoma (B cell, T cell, or neither B nor T cell derived), but not from the spleens or milk of young V+ or V- animals. The env proteins of the MCF isolates are highly heterogeneous, but most isolates originating from B10.AV + T-cell lymphomas share MCF-related epitopes in their gp85 envelope precursor with AKR MCF-247 virus. Most MCF viruses isolated from non-T lymphomas do not possess these epitopes. The results indicate that also in this model the generation of dualtropic MCF viruses might be important in lymphoma induction, although only some of the cloned MCF viruses show enhanced oncogenic properties in comparison with ecotropic isolates. A cloned oncogenic MCF virus induced different lymphoma types in C57BL/10 (= B10, H-2b) and B10.A (H-2a) mice, similar to what was found earlier with the milk-transmitted virus. Hence, the lymphoma-type differences are not due to differences in the B-tropic ecotropic viruses transmitted through the milk in these strains, but reflect an influence of the H-2 complex on the phenotype of the virus-induced lymphomas.

Thermal inactivation of human immunodeficiency virus in lyophilised blood products evaluated by ID50 titrations.

Inactivation of human immunodeficiency virus (HIV) in lyophilised small pool cryoprecipitate, factor VIII concentrate, prothrombin complex and C1-esterase inhibitor concentrate by prolonged heat treatment (72 h, 60 degrees C) was studied. Plasma products, inoculated prior to lyophilisation, had infectious titres ranging from 10(7) to 10(10.5). Residual infectivity (TCID50) was assessed by multiple titrations on H9 cells in a macro system and subsequent detection of virus replication by determining reverse transcriptase activity. Kinetics of inactivation showed a biphasic pattern: during the first 8 h a variable TCID50 reduction up to 10(4.3) was observed, followed by an additional loss of 10(1)-10(2.7) during the next 64 h. Heat treatment for 72 h resulted in a mean TCID50 reduction of 10(5). It is concluded that prolonged heat treatment may lead to the adequate prevention of HIV transmission by lyophilised plasma products.