Using lymphocyte function-associated antigen (LFA)-1−/− mice, we have examined the role of LFA-1 and other integrins in the recirculation of lymphocytes. LFA-1 has a key role in migration to peripheral lymph nodes (pLNs), and influences migration into other LNs. Second, the α4 integrins, α4β7 and α4β1, have a hitherto unrecognized ability to compensate for the lack of LFA-1 in migration to pLNs. These findings are confirmed using normal mice and blocking LFA-1 and α4 monoclonal antibodies. Unexpectedly, vascular cell adhesion molecule (VCAM)-1, which is essential in inflammatory responses, serves as the ligand for the α4 integrins on pLN high endothelial venules. VCAM-1 also participates in trafficking into mesenteric LNs and Peyer's patch nodes where mucosal addressin cell adhesion molecule 1 (MAdCAM-1), the α4β7-specific ligand, dominates. Both α4β1, interacting with ligand VCAM-1, and also LFA-1 participate in substantial lymphocyte recirculation through bone marrow. These observations suggest that organ-specific adhesion receptor usage in mature lymphocyte recirculation is not as rigidly adhered to as previously considered, and that the same basic sets of adhesion receptors are used in both lymphocyte homing and inflammatory responses.

Early neutrophil entry into an inflammatory site is thought to mediate a chemokine switch, inducing subsequent monocyte recruitment through the regulation of monocyte chemoattractant protein-1 (MCP-1) release. As the murine monocyte is poorly characterized and difficult to identify, there has been little examination of either its early recruitment in inflammatory models or of the factors that influence its early migration. The phenotyping of rapidly recruited inflammatory leukocytes with 7/4 and Gr-1 monoclonal antibodies (mAbs) identifies 2 distinct populations, which we characterize as murine monocytes and neutrophils. Monocytes migrate in the first 2 hours of inflammation making use of ␣4␤1 but not of Mac-1 or lymphocyte function-associated antigen-1 (LFA-1)

After injury or infection, neutrophils rapidly migrate from the circulation into tissues by means of an orderly progression of adhesion receptor engagements. Neutrophils have been previously considered to use selectins exclusively to roll on vessels before an adhesion step mediated by the β2 integrins, lymphocyte function–associated antigen (LFA)-1, and Mac-1. Here we use LFA-1−/− mice, function blocking monoclonal antibodies, and intravital microscopy to investigate the roles of LFA-1, Mac-1, and α4 integrins in neutrophil recruitment in vivo. For the first time, we show that LFA-1 makes a contribution to neutrophil rolling by stabilizing the transient attachment or tethering phase of rolling. In contrast, Mac-1 does not appear to be important for either rolling or firm adhesion, but instead contributes to emigration from the vessel. Blocking Mac-1 in the presence of LFA-1 significantly reduces emigration, suggesting cooperation between these two integrins. Low levels of α4β1 integrin can be detected on neutrophils from LFA-1+/+ and −/− mice. These cells make use of α4β1 during the rolling phase, particularly in the absence of LFA-1. Thus LFA-1 and α4β1, together with the selectins, are involved in the rolling phase of neutrophil recruitment, and, in turn, affect the later stages of the transmigration event.

The nature of the antibodies produced by the rabbit during the primary and secondary responses to T2 phage, proteins, and the O and H antigens of Salmonella typhosa has been determined. Immune sera have been fractionated by zone electrophoresis, sucrose density ultracentrifugation, and anion exchange chromatography. The resulting fractions have been assayed by phage neutralization or hemagglutination (antisera to proteins) or bacterial agglutination. In confirmation and extension of earlier work from this laboratory, the primary response to these antigens, with the exception of the O antigen of the Salmonella, included the early synthesis of 19S, γ-1 globulin antibody, and the later synthesis of 7S, γ-2 globulin antibody. The primary response to the O antigen consisted of the synthesis of only a macroglobulin agglutinin. The secondary response to the proteins, including the H antigen of the Salmonella, comprised the early synthesis of large amounts of the 7S γ-2 globulin antibody to the same level attained during the primary response. The secondary response to the phage consisted in the synthesis of 7S, γ-2 globulin antibody alone. Treatment of the macroglobulin phage-neutralizing antibody with mercaptoethanol resulted in complete loss of its neutralizing activity. A working hypothesis to explain these observations was presented. A salient feature of this hypothesis was the suggestion that different cells synthesized the two distinct molecular forms of antibody. The significance of the sequential synthesis of the two forms of antibody is not known. It was proposed that the system for synthesis of macroglobulin antibody is an auxiliary system for antibody synthesis, perhaps the first to develop phylogenetically and ontogenetically. It is felt that the present observations indicate a clear-cut qualitative distinction between the primary and secondary responses to immunization whereby these responses might be identified in various experimental situations. It is also felt that these findings with the primary and secondary responses to various antigens in the rabbit may be of widespread occurrence in nature among a variety of species.