Evolution by the birth-and-death process in multigene families of the vertebrate immune system

Concerted evolution is often invoked to explain the diversity and evolution of the multigene families of major histocompatibility complex (MHC) genes and immunoglobulin (Ig) genes. However, this hypothesis has been controversial because the member genes of these families from the same species are not necessarily more closely related to one another than to the genes from different species. To resolve this controversy, we conducted phylogenetic analyses of several multigene families of the MHC and Ig systems. The results show that the evolutionary pattern of these families is quite different from that of concerted evolution but is in agreement with the birth-and-death model of evolution in which new genes are created by repeated gene duplication and some duplicate genes are maintained in the genome for a long time but others are deleted or become nonfunctional by deleterious mutations. We found little evidence that interlocus gene conversion plays an important role in the evolution of MHC and Ig multigene families.

Fas (CD95) expression and death-mediating function are induced by CD4 cross-linking on CD4+ T cells.

The CD4 receptor contributes to T-cell activation by coligating major histocompatibility complex class II on antigen presenting cells with the T-cell receptor (TCR)/CD3 complex, and triggering a cascade of signaling events including tyrosine phosphorylation of intracellular proteins. Paradoxically, CD3 cross-linking prior to TCR stimulation results in apoptotic cell death, as does injection of anti-CD4 antibodies in vivo of CD4 ligation by HIV glycoprotein (gp) 120. In this report we investigate the mechanism by which CD4 cross-linking induces cell death. We have found that CD4 cross-linking results in a small but rapid increase in levels of cell surface Fas, a member of the tumor necrosis factor receptor family implicated in apoptotic death and maintenance of immune homeostasis. Importantly, CD4 cross-linking triggered the ability of Fas to function as a death molecule. Subsequent to CD4 cross-linking, CD4+ splenocytes cultured overnight became sensitive to Fas-mediated death. Death was Fas-dependent, as demonstrated by cell survival in the absence of plate-bound anti-Fas antibody, and by the lack of CD4-induced death in cells from Fas-defective lymphoproliferative (lpr) mice. We demonstrate here that CD4 regulates the ability of Fas to induce cell death in Cd4+ T cells.

In vivo estimates of division and death rates of human T lymphocytes.

We present data on the decay, after radiotherapy, of naive and memory human T lymphocytes with stable chromosome damage. These data are analyzed in conjunction with existing data on the decay of naive and memory T lymphocytes with unstable chromosome damage and older data on unsorted lymphocytes. The analyses yield in vivo estimates for some life-history parameters of human T lymphocytes. Best estimates of proliferation rates have naive lymphocytes dividing once every 3.5 years and memory lymphocytes dividing once every 22 weeks. It appears that memory lymphocytes can revert to the naive phenotype, but only, on average, after 3.5 years in the memory class. The lymphocytes with stable chromosome damage decay very slowly, yielding surprisingly low estimates of their death rate. The estimated parameters are used in a simple mathematical model of the population dynamics of undamaged naive and memory lymphocytes. We use this model to illustrate that it is possible for the unprimed subset of a constantly stimulated clone to stay small, even when there is a large population of specific primed cells reverting to the unprimed state.

First things and last : the story of birth and death certificates.

Cover title.

Remarks on the life and death of the fam'd Mr. Blood : giving an account [brace]of his plot in Ireland, to surprize Dublin Castle; several transactions in his head-quarters in the city; rescue of Captain Mason at Doncaster; attempt on the person of his Grace the Duke of Ormond; seizing on the crown and scepter in the Tower; coming into favour with his Prince; concern about his Grace the Duke of Buckingham; sickness, death, and twice interment : published for publick information.

Leaf A₂ mis-signed as A₁.

The life and death of Louis XVI,

Plan on lining-papers.

The holy death : a critical exposition of all that is told us in the New Testament concerning the trial, condemnation and death of Jesus of Nazareth /

Mode of access: Internet.

Facts of life and death.

Mode of access: Internet.

Price and purity of cocaine : the relationship to emergency room visits and death, and to drug use among arrestees.

"October 1992"--Cover.

The complete works of R. Southwell : with life and death.

"Memoir of the Rev. Robert Southwell, S. J.": p. [vii]-xxiv.

Material relating to retirement and death benefit system University of Illinois.

Includes tables of benefits.

Recommendations relating to retirement and death benefit system of the University of Illinois.

Includes tipped in "Digest of legislative bill for University retirement system".

The life and death of Lord Edward Fitzgerald.

Mode of access: Internet.

An account of the gospel labours, and Christian experiences of a faithful minister of Christ, John Churchman, late of Nottingham, in Pennsylvania, deceased. To which is added, A short memorial of the life and death of a fellow labourer in the church, our valuable friend Joseph White, late of Bucks county ...

Running title: The life and travels of John Churchman.

Memoirs of Napoleon Bonaparte. To which are now first added an account of the important events of the hundred days, of Napoleon's surrender to the English, and of his residence and death at St. Helena, with anecdotes and illustrative notes from all the most authentic sources.

Mode of access: Internet.