Retroviral infection of neonatal Peyer's patch lymphocytes: the mouse mammary tumor virus model.

Mouse mammary tumor virus is known to infect newborn mice via mother's milk. A proposed key step for viral spread to the mammary gland is by the infection of lymphocytes. We show here that although in suckling mice retroviral proteins are found in all epithelial cells of the gut, viral DNA is exclusively detectable in the Peyer's patches. As early as 5 d after birth the infection leads to a superantigen response in the Peyer's patches but not in other lymphoid organs draining the intestine. Viral DNA can be detected before the superantigen response and becomes first evident in the Peyer's patches followed by mesenteric lymph nodes and finally all lymphoid organs

The membrane receptor for polymeric immunoglobulin is structurally related to secretory component. Isolation and characterization of membrane secretory component from rabbit liver and mammary gland.

The membrane receptor of epithelial cells which binds polymeric immunoglobulins and mediates their transepithelial translocation is antigenically related to secretory component (SC), a glycoprotein produced by the epithelial cells. In rabbit milk, secreted SC is found either bound to polymeric immunoglobulin A (IgA) or in a free form. It is comprised of a heterogeneous population of molecules with apparent Mr = 83,000 and 80,000 (upper doublet) and 58,000 and 55,000 (lower doublet). Membrane SC was isolated by immunoadsorption from deoxycholate-solubilized plasma membranes of rabbit liver and mammary gland. The purified proteins, heterogenous in size with apparent Mr = 120,000 and 116,000 (upper doublet) and 95,000 and 91,000 (lower doublet), were amphiphilic. One-dimensional peptide maps revealed extensive structural homology between both the upper doublets of the membrane and secreted SC, as well as between the lower doublets. This indicates that the high Mr membrane SC of hepatocytes and mammary cells are precursors of the lower Mr secreted SC found in bile and milk. All four membrane SC, purified in high yield from rabbit liver by immunoadsorption and preparative electrophoresis in the presence of sodium dodecyl sulfate, bound IgA dimer specifically. The affinity (Kd approximately equal to 10 nM) was similar to the one observed in free SC-IgA dimer interaction. Only the membrane proteins recognized by the anti-SC antibodies were able to bind polymeric IgA. In liver membrane preparations, the receptor was localized at the surface of smooth vesicles, using IgA dimer-biotin and avidin-gold. Our results indicate that the high Mr membrane SC is the plasma membrane receptor for polymeric immunoglobulin

Interaction of rabbit secretory component with rabbit IgA dimer.

Secretory component (SC), a glycoprotein with an apparent molecular weight of approximately 80,000, has been isolated from rabbit milk and found to be heterogenous in size and charge. Functionally intact IgA dimer has been dissociated from milk secretory IgA using a chaotropic agent and further purified to homogeneity. The interaction between SC and IgA dimer is a reversible time- and temperature-dependent process. At 23 degrees C, the association rate constant (2.4 x 10(5) M-1 min-1) and the dissociation rate constant (1.8 x 10(-3) min-1) have been measured independently and the affinity constant based on these rates (1.3 x 10(8) M-1) is similar to that calculated from Scatchard plots (1.9 x 10(8) M-1). One class of binding sites has been estimated from Scatchard plots in spite of the observed heterogeneity of SC. The interaction is tighter at low temperatures because the decrease in dissociation rate is greater than the decrease in association rate. The thermodynamic calculations reveal a delta G of -11.0 kcal . mol-1, a delta H of -8.9 kcal . mol-1 and a delta S of +7.0 cal. mol-1 degree-1. The pH range over which interaction occurs is rather large (5 to 8) with no significant differences in apparent Ka

Recombinant fusion peptides containing single or multiple repeats of a ubiquitous T-helper epitope are highly immunogenic.

Two recombinant mouse mammary tumor virus (MMTV) subunit vaccines have been constructed, in which linear sequences of the envelope gp 52 glycoprotein (EP3) or the superantigen (SAg) have been fused to single or multiple repeats of a T-cell epitope (P30) from tetanus toxin. Histidine tags or glutathione-S-transferase (GST) sequences have been included in the recombinant peptides in order to facilitate their purification by affinity chromatography. The EP3 or SAg recombinant polypeptides with four, one, or no T-cell epitopes were expressed in Escherichia coli, purified and injected intramuscularly, with non-ionic block copolymers as an adjuvant, into BALB/c mice. Following one or two boosts, the B- and T-cell responses against the recombinant proteins were analysed. The addition of T-cell epitopes considerably increased the immunogenicity of the subunit vaccines. The anti-EP3 response was maximum with four T-cell epitopes, while a single T epitope was optimal for the anti-SAg response