Jennifer Bell

New family ties to asthma

It seems that vaccine development has never had such a high profile. With vaccines available against smallpox and anthrax, how exactly they should be used to combat the threat of bioterrorism has been a subject of debate in the US press. A feature in The Washington Post pointed out that existing vaccines to potential bioterrorism agents were “developed decades ago and can cause severe side effects or even death” and advised its readers against investing in vaccine development. Although acknowledging the risks, Warren Leary, writing in The New York Times, advocated voluntary vaccination against smallpox — “even if only part of the population were vaccinated, the bang for the terrorist’s buck could be drastically curtailed”. Meanwhile, ongoing efforts to develop vaccines for the big killers — HIV, malaria and tuberculosis — have not hit the headlines. Although the BBC World Service did report on a “promising” new malaria vaccine undergoing clinical trial in the Gambia. The lowkey tone was perhaps appropriate given that the vaccine only protected 47% of individuals. Another report from the BBC News provided a timely warning that “Weak vaccines strengthen disease”. This story covered the predictions of Edinburghbased epidemiologists (originally published in Nature 13 December 2001) that, in the case of chronic diseases, such as malaria, vaccines that are less than 100% effective have the potential to do more harm than good. Specifically, vaccines that only protect a proportion of the population could lead to outbreaks of more virulent forms of disease and the news article claims that this “could kill more people that any vaccination programme would save”. Jennifer Bell IN THE NEWS

Signalling: Build your own B cell

Our map of antigen-receptor signalling pathways is based largely on studies in which the function of signalling molecules was disrupted. This knockout approach allows the ordering of components in a pathway, but it can tell us little about feedback mechanisms that might exist. This led Rolli and colleagues at the University of Freiburg to devise an alternative approach — the reconstruction of B-cell receptor (BCR) signalling pathways in Drosophila cells. The new system has produced some surprising results, which are reported in Molecular Cell. Interference from endogenous signalling pathways is a potential problem when expressing receptors and signalling components in another vertebrate cell type. To minimize this, Rolli et al. used Drosophila Schneider S2 cells. These cells are used commonly for large-scale protein production, so it was probable that they would be able to ‘cope’ with the cotransfection of several foreign genes. Expression vectors containing a copper-sulphate-inducible promoter were used to express the BCR and various signalling components in S2 cells. According to present models, BCR signal transduction is initiated by phosphorylation of the two tyrosine residues in the ITAMs (immunoreceptor tyrosine-based activation motifs) of Igα/β (the paired signalling subunits of the BCR) by the membrane-associated SRC-family protein tyrosine kinase (PTK) LYN. This is thought to allow recruitment of the cytosolic PTK SYK and activation of downstream effector enzymes. But, by transfecting S2 cells with the BCR and various combinations of wildtype or mutated forms of Igα/β, LYN and SYK, the authors found that LYN tends to phosphorylate only the first tyrosine of the ITAM, whereas SYK can phosphorylate both tyrosines. Therefore, SYK can phosphorylate the BCR independent of LYN, and it is a more probable candidate for the first step in BCR signal transduction. Further experiments showed that the SRC-homology 2 (SH2) domains of SYK, which bind to phosphorylated ITAMs, are required to optimize the activity of its catalytic domain. This implies that SYK can regulate its own activity, because its product — phosphorylated ITAMs — induces the further activation and recruitment of SYK. This positivefeedback loop has the potential to

Build your own B cell: Signalling

Our map of antigen-receptor signalling pathways is based largely on studies in which the function of signalling molecules was disrupted. This knockout approach allows the ordering of components in a pathway, but it can tell us little about feedback mechanisms that might exist. This led Rolli and colleagues at the University of Freiburg to devise an alternative approach — the reconstruction of B-cell receptor (BCR) signalling pathways in Drosophila cells. The new system has produced some surprising results, which are reported in Molecular Cell. Interference from endogenous signalling pathways is a potential problem when expressing receptors and signalling components in another vertebrate cell type. To minimize this, Rolli et al. used Drosophila Schneider S2 cells. These cells are used commonly for large-scale protein production, so it was probable that they would be able to ‘cope’ with the cotransfection of several foreign genes. Expression vectors containing a copper-sulphate-inducible promoter were used to express the BCR and various signalling components in S2 cells. According to present models, BCR signal transduction is initiated by phosphorylation of the two tyrosine residues in the ITAMs (immunoreceptor tyrosine-based activation motifs) of Igα/β (the paired signalling subunits of the BCR) by the membrane-associated SRC-family protein tyrosine kinase (PTK) LYN. This is thought to allow recruitment of the cytosolic PTK SYK and activation of downstream effector enzymes. But, by transfecting S2 cells with the BCR and various combinations of wildtype or mutated forms of Igα/β, LYN and SYK, the authors found that LYN tends to phosphorylate only the first tyrosine of the ITAM, whereas SYK can phosphorylate both tyrosines. Therefore, SYK can phosphorylate the BCR independent of LYN, and it is a more probable candidate for the first step in BCR signal transduction. Further experiments showed that the SRC-homology 2 (SH2) domains of SYK, which bind to phosphorylated ITAMs, are required to optimize the activity of its catalytic domain. This implies that SYK can regulate its own activity, because its product — phosphorylated ITAMs — induces the further activation and recruitment of SYK. This positivefeedback loop has the potential to

Build your own B cell

Our map of antigen-receptor signalling pathways is based largely on studies in which the function of signalling molecules was disrupted. This knockout approach allows the ordering of components in a pathway, but it can tell us little about feedback mechanisms that might exist. This led Rolli and colleagues at the University of Freiburg to devise an alternative approach — the reconstruction of B-cell receptor (BCR) signalling pathways in Drosophila cells. The new system has produced some surprising results, which are reported in Molecular Cell. Interference from endogenous signalling pathways is a potential problem when expressing receptors and signalling components in another vertebrate cell type. To minimize this, Rolli et al. used Drosophila Schneider S2 cells. These cells are used commonly for large-scale protein production, so it was probable that they would be able to ‘cope’ with the cotransfection of several foreign genes. Expression vectors containing a copper-sulphate-inducible promoter were used to express the BCR and various signalling components in S2 cells. According to present models, BCR signal transduction is initiated by phosphorylation of the two tyrosine residues in the ITAMs (immunoreceptor tyrosine-based activation motifs) of Igα/β (the paired signalling subunits of the BCR) by the membrane-associated SRC-family protein tyrosine kinase (PTK) LYN. This is thought to allow recruitment of the cytosolic PTK SYK and activation of downstream effector enzymes. But, by transfecting S2 cells with the BCR and various combinations of wildtype or mutated forms of Igα/β, LYN and SYK, the authors found that LYN tends to phosphorylate only the first tyrosine of the ITAM, whereas SYK can phosphorylate both tyrosines. Therefore, SYK can phosphorylate the BCR independent of LYN, and it is a more probable candidate for the first step in BCR signal transduction. Further experiments showed that the SRC-homology 2 (SH2) domains of SYK, which bind to phosphorylated ITAMs, are required to optimize the activity of its catalytic domain. This implies that SYK can regulate its own activity, because its product — phosphorylated ITAMs — induces the further activation and recruitment of SYK. This positivefeedback loop has the potential to

Immunological memory: How T cells survive

Much as plants compete for essential resources such as space, sunlight, water and nutrients, so peripheral T cells compete for limited growth and survival signals, which keeps the overall population size remarkably constant. The factors that regulate the size of the memory CD4 T-cell pool have long been a mystery, but a new study shows that the answer was under our noses all along. Different T-cell subsets depend on distinct survival signals and, in this way, competition for the same ‘niche’ is avoided. Interleukin-7 (IL-7) and contact with MHC class I or MHC class II molecules are thought to maintain the naive CD8 and CD4 T-cell pools, whereas memory CD8 T cells require IL-7 and IL-15. But none of these factors seems to be required for the survival of memory CD4 T cells. Benedict Seddon and colleagues decided to revisit this issue. First, the role of T-cell receptor (TCR) signals was investigated using mice deficient in both Lck and Fyn (crucial components of TCR signalling) that carried an inducible Lck transgene. When Lck was switched on, normal memory and naive T-cell compartments were generated. When the transgene was switched off, the naive CD4 T cells disappeared, but the memory-phenotype CD4 T cells survived, confirming previous reports that TCR signals are not required for the survival of memory T cells. Previous studies have also ruled out a requirement for IL-7. But, what happens when both IL-7 and TCR signals are lacking? Lck-deficient memory CD4 T cells were transferred to lymphocyte deficient Il7 Rag1 mice. The transferred cells failed to divide and few were recovered compared with similar transfers to Il7 Rag1 mice. This

Antiviral immunity: Dengue's deadly second sting

Much as plants compete for essential resources such as space, sunlight, water and nutrients, so peripheral T cells compete for limited growth and survival signals, which keeps the overall population size remarkably constant. The factors that regulate the size of the memory CD4 T-cell pool have long been a mystery, but a new study shows that the answer was under our noses all along. Different T-cell subsets depend on distinct survival signals and, in this way, competition for the same ‘niche’ is avoided. Interleukin-7 (IL-7) and contact with MHC class I or MHC class II molecules are thought to maintain the naive CD8 and CD4 T-cell pools, whereas memory CD8 T cells require IL-7 and IL-15. But none of these factors seems to be required for the survival of memory CD4 T cells. Benedict Seddon and colleagues decided to revisit this issue. First, the role of T-cell receptor (TCR) signals was investigated using mice deficient in both Lck and Fyn (crucial components of TCR signalling) that carried an inducible Lck transgene. When Lck was switched on, normal memory and naive T-cell compartments were generated. When the transgene was switched off, the naive CD4 T cells disappeared, but the memory-phenotype CD4 T cells survived, confirming previous reports that TCR signals are not required for the survival of memory T cells. Previous studies have also ruled out a requirement for IL-7. But, what happens when both IL-7 and TCR signals are lacking? Lck-deficient memory CD4 T cells were transferred to lymphocyte deficient Il7 Rag1 mice. The transferred cells failed to divide and few were recovered compared with similar transfers to Il7 Rag1 mice. This

The art of joining

In 1980, the World Health Organisation declared that smallpox had been eradicated, but two stocks of the virus remain and smallpox is still of concern owing to potential use of the causative agent variola virus in bioterrorism. It was the work of the English physician Edward Jenner (1749–1823) that led to the development of a vaccine and the subsequent eradication of smallpox. If you want to find out more about Edward Jenner, a good place to start might be the web site of The Jenner Museum in Gloucestershire, which was opened to the public in 1985. This web site details the life and work of Edward Jenner, from his early life in Gloucestershire to his famous work on smallpox — or as Jenner called it ‘the speckled monster’ — and vaccination. Jenner’s work on cowpox as a vaccine for smallpox led to the introduction of compulsory vaccination in 1853. There are some intriguing additional titbits about some of Jenner’s other interests, including fossils, hibernation of hedgehogs and the nesting habits of cuckoos. You can also take a look at his family tree and find out what the museum facilities have to offer for visiting student groups. The site is a useful educational resource for all ages — one section provides basic background information on the human immune system, vaccination, transplantation and defects in immunity, and a glossary of terms. This section also includes a topical opinion poll with questions about vaccination that should be useful for stimulating discussion. By answering the questions, you can access the poll results so far. Check the web site for further information! Elaine Bell WEB WATCH

Lymphocyte development: The art of joining

In 1980, the World Health Organisation declared that smallpox had been eradicated, but two stocks of the virus remain and smallpox is still of concern owing to potential use of the causative agent variola virus in bioterrorism. It was the work of the English physician Edward Jenner (1749–1823) that led to the development of a vaccine and the subsequent eradication of smallpox. If you want to find out more about Edward Jenner, a good place to start might be the web site of The Jenner Museum in Gloucestershire, which was opened to the public in 1985. This web site details the life and work of Edward Jenner, from his early life in Gloucestershire to his famous work on smallpox — or as Jenner called it ‘the speckled monster’ — and vaccination. Jenner’s work on cowpox as a vaccine for smallpox led to the introduction of compulsory vaccination in 1853. There are some intriguing additional titbits about some of Jenner’s other interests, including fossils, hibernation of hedgehogs and the nesting habits of cuckoos. You can also take a look at his family tree and find out what the museum facilities have to offer for visiting student groups. The site is a useful educational resource for all ages — one section provides basic background information on the human immune system, vaccination, transplantation and defects in immunity, and a glossary of terms. This section also includes a topical opinion poll with questions about vaccination that should be useful for stimulating discussion. By answering the questions, you can access the poll results so far. Check the web site for further information! Elaine Bell WEB WATCH

The art of joining: Lymphocyte development

In 1980, the World Health Organisation declared that smallpox had been eradicated, but two stocks of the virus remain and smallpox is still of concern owing to potential use of the causative agent variola virus in bioterrorism. It was the work of the English physician Edward Jenner (1749–1823) that led to the development of a vaccine and the subsequent eradication of smallpox. If you want to find out more about Edward Jenner, a good place to start might be the web site of The Jenner Museum in Gloucestershire, which was opened to the public in 1985. This web site details the life and work of Edward Jenner, from his early life in Gloucestershire to his famous work on smallpox — or as Jenner called it ‘the speckled monster’ — and vaccination. Jenner’s work on cowpox as a vaccine for smallpox led to the introduction of compulsory vaccination in 1853. There are some intriguing additional titbits about some of Jenner’s other interests, including fossils, hibernation of hedgehogs and the nesting habits of cuckoos. You can also take a look at his family tree and find out what the museum facilities have to offer for visiting student groups. The site is a useful educational resource for all ages — one section provides basic background information on the human immune system, vaccination, transplantation and defects in immunity, and a glossary of terms. This section also includes a topical opinion poll with questions about vaccination that should be useful for stimulating discussion. By answering the questions, you can access the poll results so far. Check the web site for further information! Elaine Bell WEB WATCH

Mint-flavoured B cells

How is tolerance to organ-specific antigens maintained? It was assumed originally that tolerance depends mainly on immunological ‘ignorance’ or peripheral regulatory mechanisms. However, evidence that organspecific antigens are expressed by rare thymic medullary epithelial cells has indicated that central-tolerance mechanisms might be important also. Humans with autoimmune polyendocrinopathy syndrome type 1 — which results from mutations in the autoimmune regulator (AIRE) gene — develop a range of organspecific autoimmune diseases. Chris Goodnow and colleagues are the first to show that self-tolerance might be defective in these patients owing to a failure of negative selection in the thymus. As AIRE seems to be a transcriptional regulator and is expressed mainly by rare thymic stromal cells, this protein is likely to be important for the thymic expression of otherwise organ-specific antigens and their role in central tolerance. In T-cell receptor (TCR)-transgenic 3A9-insHEL mice, which produce T cells with specificity for hen egg lysozyme (HEL) and express HEL under control of the rat insulin promoter, the TCR-transgenic T cells are deleted in the thymus as a result of thymic antigen expression. To analyse the effects of Aire on this process, the TCR-transgenic mice were crossed with Aire-mutant mice. No difference was observed in the positive selection of TCRtransgenic T cells between Aire and Aire mice that lacked expression of insHEL. In Aire 3A9insHEL mice, few CD4 T cells were present, indicating efficient negative selection, and those T cells that remained were anergic. However, in Aire 3A9-insHEL mice, normal numbers of mature CD4 T cells were produced, indicating a failure of thymic deletion. Reconstitution experiments were used to determine the lineage requirements for expression of Aire. Aire T cells were deleted normally in the thymi of Aire mice, whereas Aire