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Core pentapeptides and an octapeptide (Peptide T) computer deduced from amino acid sequences from vasoactive intestinal peptide (VIP) and the 120 gp external envelope of the HIV (AIDS) virus and synthesized have been reported to have important in vitro and in vivo activity including inhibition of HIV binding to CD4 surface antigens of brain cells and lymphocytes and limitation of HIV infectivity. Two of these core pentapeptides, peptide TTNYT (Peptide T [4-8]) and peptide TDNYT (VIP [7-11]), are reported here, on acute infusion into cannulated afferent popliteal lymphatics of sheep, to produce prompt and marked depressions in the output of both small recirculating and blast lymphocytes into popliteal lymph node efferent lymph. As with a prior VIP infusion study, there appeared to be a selective effect on T4 (CD4) lymphocytes, with a marked predominance of T4 (CD4) lymphocytes in the lymphocyte depleted efferent lymph.

Induced systemic arterial hypotension by intravenous nitroprusside administration and by acute arterial occlusion in sheep have been found to reduce lymphocyte traffic as mirrored in the output of lymphocytes into the efferent lymph of peripheral lymph nodes. In the present series of experiments in sheep with chronically cannulated efferent lymphatics of peripheral lymph nodes, induced and monitored systemic arterial hypertension with intravenous pump infusions of phenylephrine or dopamine both produced sharp increases in the output of lymphocytes into efferent lymph in all of 27 studies. The increases in lymphocyte output with dopamine were more sustained and less associated with evidence of lymphoid tissue damage than with phenylephrine. Phenylephrine infusions were attended by a high incidence of gross bleeding into the efferent lymph, of increased coagulability of efferent lymph in the absence of gross bleeding and of prolonged depression of lymphocyte outputs after the cessation of intravenous infusion.

In the past decade, the main interest in the involvement of prostaglandin E2 (PGE2) in the immune response has been concerned with its role in immunomodulation (suppression) both in vitro and in vivo. Comparatively little attention has been devoted to its immunostimulatory role. It has been suggested that PGE2, like histamine, may function as a 'double agent', initially triggering, facilitating and augmenting a stimulatory immune response and later modulating, limiting and contributing to the turning off of this response. We here report an early (within minutes) immunostimulatory involvement of PGE2 (and thromboxane A2) in the sheep, with prompt elevations in levels of PGE2 and thromboxane B2 in popliteal lymph node efferent lymph following drainage area immunization with killed Salmonella muenchen bacteria. These elevations were associated with an increase in efferent lymph flow and an equally prompt but limited depression of lymphocyte outputs into efferent lymph ('shutdown', 'recruitment'). Local increases in blood flow and vascular permeability probably play important roles in these events.