AIDS in chimpanzees: the role of MHC genes
Natasja G. de Groot
Corinne M. C. Heijmans
Ronald E. Bontrop
Received: 26 May 2017 /Accepted: 27 May 2017 /Published online: 10 July 2017
Springer-Verlag Berlin Heidelberg 2017
Abstract The ancestral progenitor of common chimpanzees
and bonobos experienced a selective sweep that ravaged its
major histocompatibility complex (MHC) class I repertoire.
The causative agent was probably an ancestral retrovirus,
highly related to the contemporary HIV-1 strain, which initi-
ated the acquired immunodeficiency syndrome pandemic in
the human population. As a direct result, MHC class I allo-
types with the capability of targeting conserved retroviral ele-
ments were enriched in the ancestral progenitor. Even today,
the impact can be traced back by studying the functional ca-
pacities of the contemporary MHC class I allotypes of com-
mon chimpanzees. Viruses, however, have developed several
strategies to manipulate the cell-surface expression of MHC
class I genes. Monitoring the presence and absence of the
MHC class I allotypes on the cell surface is conducted, for
instance, by the hosts’ gene products of the killer cell
immunoglobulin-like receptor (KIR) complex. Hence, one
may wonder whether—in the future—any clues with regard
to the signature of the MHC class I selective sweep might be
unearthed for the KIR genes as well.
The evolutionary history of humans
The cradle of mankind lies in Africa, with the first wave of
migration by early humans (Homo erectus) taking place about
1.9 million years ago. In their turn, modern humans (Homo
sapiens) migrated out of Africa roughly 100,000 years ago,
and successfully conquered most of the world, including be-
coming established in very hostile environments (Mallick et al.
2016; Nielsen et al. 2017). Chimpanzees and modern humans
are each other’s closest living relatives, and both species shared
a common ancestor that lived approximately 5 million years
ago. Two species of chimpanzees are officially recognised,
namely the common chimpanzee (Pan troglodytes)—hereafter
referred to as chimpanzee—and the bonobo (Pan paniscus).
Based on their geographic distribution in Africa, and on mor-
phological and genetic data, chimpanzees have been clustered
into four different subspecies, namely West African (P. t .
verus), Central African (P.t. troglodytes), East African (P.t.
schweinfurthii) and the Nigerian/Cameroon (P.t. ellioti), which
radiated almost 1.5 million years ago (Bowden et al. 2012;
Gagneux et al. 1999). Bonobos have a far more restricted hab-
itat, and live in the forests south of the Congo River. The
common ancestor of bonobos and chimpanzees wandered
through Central Africa around 2 million years ago, and there
is evidence for an ancient admixture between both chimpanzee
species (de Manuel et al. 2016). For convenience, the data
mentioned above are summarised in Fig. 1.
The close genetic relationship of humans and chimpanzees
is reflected by the fact that they share 98.7% sequence simi-
larity at the primary DNA level (Prado-Martinez et al. 2013).
One should realise, however, that both species differ for about
5% at the level of insertions and deletions (indels), thus im-
plying that genes that are present in one species may be absent
in the other (Britten 2002; Wetterbom et al. 2006). Although
This article is published in the Special Issue MHC Genes and Their
Ligands in Health and Disease with Editor Prof. Ronald Bontrop.
* Natasja G. de Groot
Comparative Genetics and Refinement, Biomedical Primate
Research Centre, 2288 GJ Rijswijk, The Netherlands
Theoretical Biology and Bioinformatics, Utrecht University, 3584
CH Utrecht, The Netherlands
Immunogenetics (2017) 69:499–509