C O M M E N T is the 'attachment' molecule then in- creased binding would be observed in the Lcr5 cells. However, a sec- ondary role would be suggested if binding is equivalent after adsorp- tion at 4°C and the 10-fold differ- ence only became evident by shifting to 37°C; in other words, HAVcr-1 may be an accessory factor prevent- ing elution from a ubiquitous re- ceptor. Second, the calcium depend- ence of HAV binding to Lcr5 and LDR2 cells should be determined. If the binding of HAV to LDR2 cells was nonspecific, as the authors speculate, then adsorption would be calcium independent. Conversely, Lcr5 cells would exhibit calcium- dependent binding of HAV. How- ever, if the level is equivalent for both cell lines it would suggest that HAVcr-1 has a role after this initial binding step. It is hoped that further work will define the precise role of HAVcr-1 in HAV replication, both in cell culture and natural hosts. Raquel U. Cowan and David A. Anderson Macfarlane Burnet Centre for Medical Research, Fairfield Hospital, Fairfield, Victoria 3078, Australia References 1 Stapleton, J.T., Frederick, J. and Meyer, B. (1991)J. Infect. Dis. 164, 1098-1103 2 Zajac,A.J. et al. (1991) J. Gen. Virol. 72, 1667-1675 3 Kaplan,G. et al. (1996) EMBO J. 15, 4282-4296 4 Haywo0d, A.M. (1994)J. Virol. 68, 1-5 Events Of genes and germs Michel Brahic and Jean-Francois Bureau T he apparent resurgence of in- fectious diseases during the past 20 years coincides with spectacular advances in human gen- etics that make it possible to locate and identify genes involved in com- mon multifactorial diseases. Conse- quently, the role of the host genetic background in the susceptibility to infectious diseases can now be re- examined with new tools. The recent meeting held at the Pasteur Insti- tute to cover this topic was indeed timely. Identification of a genetic com- ponent in a disease can be diffi- cult, as discussed by Alain Dessein (INSERM, Marseilles, France). In an area of Brazil that is endemic for schistosomiasis, a detailed epi- demiological study showed that en- vironmental factors explained only 20% of the variance in parasite load. Laurent Abel (INSERM, Paris, France) showed that a single locus with co-dominant transmission was involved. To do this, he had to per- form a segregation analysis with corrections for environmental fac- tors. A complete genome scan, car- ried out on DNA from 20 families, linked the level of infestation to a region on chromosome 5 that codes for CSF-1R (colony-stimulating The First Louis Pasteur Conference: Genetics of the Susceptibility to Infectious Diseases, Institut Pasteur, Paris, France, 21-23 October 1996. M. Brahic * and J-F. Bureau are in the Unite des Virus Lents, URA CNRS 1157, Institut Pasteur, 75724 Paris Cedex 15, France. *tel: ÷33 1 45 68 87 70, fax: +33 1 40 61 31 67, e-mail: mbrahic@pasteur.fr factor 1 receptor) and interleukins 3, 4, 5, 9 and 13. Interestingly, these are cytokines implicated in the Th2- type responses. As discussed by Mark Lathrop (University of Oxford, UK), this type of parametric method is efficient for locating a gene that has a major effect. However, it requires making assumptions, in particular on the mode of inheritance. In contrast, nonparametric methods, such as sib pair analysis, are well suited to the analysis of multigenic diseases, although they require the collection of data from many families. Finally, testing candidate genes with a non- parametric method can also yield important information. Abel illus- trated this point with a study of leprosy and the occurrence of the NRAMP1 gene (see below). Copyright © 1997 Elsevier Science Ltd. All rights reserved. 0966 842X/97/$17.00 Mapping the genomes of mouse and man Genetic, physical and now 'inte- grated' maps are the tools for these studies and are constantly being re- fined. Approximately 6000 micro- satellite markers have been located on the genetic maps of mouse (William Dietrich, Harvard Uni- versity, Boston, MA, USA) and hu- man (Jean Weissenbach, Institut Pasteur, Paris and Genethon, Evry, France). The construction of physi- cal maps, by ordering the markers on overlapping yeast and bacterial artificial chromosomes or by using whole genome radiation hybrids, is advancing rapidly. Integrated maps, which give the position of individ- ual mRNA on the genetic and physi- cal maps, are the latest addition to this field. Approximately 16000 expressed sequence tags have been located on an integrated map of the human genome by a consortium of five groups. How these maps can be used to arrive at the gene was nicely illustrated by the work of Dietrich on the susceptibility of the A/J mouse to Legionella pneumo- phila. The causal gene (Ignl) was mapped to a small fraction of chromosome 13, which happened to be homologous to the region of PlI: S0966-842X(96)30041-3 TRENDS IN MJCROBIOI.OC;y 48 vo~ 5 IN(). 2 FEBRtlARY 1997