75 research outputs found
Peer influence in network markets: a theoretical and empirical analysis
Network externalities spur the growth of networks and the adoption of network goods in two ways. First, they make it more attractive to join a network the larger its installed base. Second, they create incentives for network members to actively recruit new members. Despite indications that the latter "peer effect" can be more important for network growth than the installed-base effect, it has so far been largely ignored in the literature. We address this gap using game-theoretical models. When all early adopters can band together to exert peer influence-an assumption that fits, e.g., the case of firms supporting a technical standard-we find that the peer effect induces additional growth of the network by a factor. When, in contrast, individuals exert peer influence in small groups of size n, the increase in network size is by an additive constant-which, for small networks, can amount to a large relative increase. The difference between small, local, personal networks and large, global, anonymous networks arises endogenously from our analysis. Fundamentally, the first type of networks is "tie-reinforcing," the other, "tie-creating". We use survey data from users of the Internet services, Skype and eBay, to illustrate the main logic of our theoretical results. As predicted by the model, we find that the peer effect matters strongly for the network of Skype users-which effectively consists of numerous small sub-networks-but not for that of eBay users. Since many network goods give rise to small, local networks
Identification of HIV-1 Epitopes that Induce the Synthesis of a R5 HIV-1 Suppression Factor by Human CD4+ T Cells Isolated from HIV-1 Immunized Hu-PBL SCID Mice
We have previously reported that immunization of the severe combined
immunodeficiency (SCID) mice reconstituted with human peripheral blood
mononuclear cells (PBMC) (hu-PBL-SCID mice) with inactivated human
immunodeficiency virus type-1 (HIV-1)-pulsed-autologous dendritic cells (HIV-DC)
elicits HIV-1-reactive CD4+ T cells that produce an as yet to be defined novel
soluble factor in vitro with anti-viral properties
against CCR5 tropic (R5) HIV-1
infection. These findings led us to perform studies designed to identify the lineage
of the cell that synthesizes such a factor in vitro and define the epitopes of HIV-1
protein that have specificity for the induction of such anti-viral factor. Results of
our
studies show that this property is a function of CD4+ but not
CD8+ T cells. Human
CD4+ T cells were thus recovered from the HIV-DC-immunized
hu-PBL-SCID mice
and were re-stimulated in vitro by co-culture for 2 days with
autologous adherent
PBMC as antigen presenting cells, APC previously pulsed with inactivated HIV in
IL-2-containing medium to expand HIV-1-reactive CD4+
T cells. Aliquots of these
re-stimulated CD4+ T cells were then co-cultured with
similar APC's that were
previously pulsed with 10 Ī¼g/ml of a panel of HIV peptides for
an additional 2 days,
and their culture supernatants were examined for the production of both the R5
HIV-1 suppression factor and IFN-Ī„. The data presented herein
show that the HIV-1
primed CD4+ T cells produced the R5 suppression factor in
response to a wide
variety of HIV-1 gag, env, pol, nef or vif peptides, depending on the donor of
the CD4+ T cells. Simultaneous production of human interferon
(IFN)-Ī„ was
observed in some cases. These results indicate that human
CD4+ T cells in
PBMC of HIV-1 naive donors have a wide variety of HIV-1 epitope-specific
CD4+ T
cell precursors that are capable of producing the R5 HIV-1
suppression factor upon DC-based vaccination with whole inactivated HIV-1
- ā¦