Activation of atrial muscarinic K+ channels by low concentrations ofβγ subunits of rat brain G protein

Effects of G protein subunits from rat brain on cardiac K⁺ channel was examined in single atrial cells of guinea-pig, using patch clamp techniques. We found that 10 pM concentration of rat brain subunits preparation could activate the atrial muscarine receptor-gated K⁺ channel (I_K.ACh). Neither the detergent, CHAPS, used to suspend nor the boiled preparation activated I_K.ACh. Furthermore, preincubation of subunits preparation in Mg²⁺-free solution, which easily inactivated -GTP-S, did not affect -activation of I_K.ACh. We concluded, therefore, that subunits themselves can activate I_K.ACh.Supported by the grants from the Ministry of Education, Culture and Science of Japan and from the Calcium Signal Workshop on Cardiovascular Systems     

Prostaglandin E2 Downregulates Interferon-γ-Induced Intercellular Adhesion Molecule-1 Expression via EP2 Receptors in Human Gingival Fibroblasts

In the present study, the effect of prostaglandin E₂ (PGE₂) on intercellular adhesion molecule-1 (ICAM-1) expression in interferon- (IFN-)-stimulated human gingival fibroblasts (HGF) was investigated. Addition of PGE₂ to HGF inhibited ICAM-1 expression elicited by IFN-. As PGE₂ elevated intercellular cyclic AMP (cAMP) levels in HGF in a dose-dependent fashion, the effect of dibutyryl cAMP and 8-bromo-cAMP, cAMP analogues, on IFN--elicited ICAM-1 expression was examined. Both the agents downregulated ICAM-1 expression in IFN--stimulated HGF. Next, we examined which subtype(s) of the four PGE₂ receptor subtypes (EP₁, EP₂, EP₃ and EP₄) modulated the ICAM-1 expression elicited by IFN-, using subtype-specific agonists or antagonists. An EP₂/EP₄ agonist, 11-deoxy-PGE₁, attenuated IFN--elicited ICAM-1 expression in a concentration-dependent manner. A specific EP₄ antagonist, AH-23848B, showed no effect on inhibition of IFN--elicited ICAM-1 expression by PGE₂ and 11-deoxy-PGE₁. Butaprost, an EP₂-selective agonist, mimicked inhibition of IFN--elicited ICAM-1 expression by 11-deoxy-PGE₁. An EP₃ agonist, ONO-AP-324, was inert with respect to IFN--elicited ICAM-1 expression. Sulprostone, an EP₁/EP₃ agonist, showed stimulatory effect on ICAM-1 expression elicited by IFN-. From these results, we suggest that PGE₂ downregulates IFN--induced ICAM-1 expression in HGF, primarily via EP₂ receptors by cAMP-dependent signaling pathways.     

Die optische Rotationsdispersion isolierter Paraproteine

Zusammenfassung Nach immunoelektrophoretischer Analyse eines Serums im Falle einer doppelten Proteinanomalie bei Plasmocytom werden Untersuchungsergebnisse mittels der Sedimentationsanalyse, der Stärkegelelektrophorese und der Säulenchromatographie mitgeteilt. Elektrophoretisch waren im ₂-und im ₁-Bereich wandernde Paraproteinkomponenten nachzuweisen. Weiterhin werden die Ergebnisse von Messungen der optischen Drehfähigkeit in Lösungen beider Paraproteine mitgeteilt. Durch chromatographische Fraktionierung an Ionenaustauschern gelang es, immunoelektrophoretisch reines normalesG-Protein undG-Paraprotein zu gewinnen. Nach der immunoelektrophoretischen Analyse der chromatographischen Fraktionen scheint auch eine Trennung des normalenA-Proteins von demA-Paraprotein auf diese Weise gelungen zu sein. Die Bedeutung der Ergebnisse in ihrer Beziehung zu der Konformation und Gruppenspezifität von pathologischen Immunglobulinen werden diskutiert.

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Summary After immunoelectrophoretic analysis of the serum from a patient suffering from multiple myeloma with a double protein anomaly (G- andA-paraprotein in one patient) sedimentation-analyses, starch gel electrophoresis and column chromatography on DEAE Sephadex A 50 of serum and isolated paraproteins were performed. Electrophoretically paraprotein components moving in the ₂- und ₁-region were observed. The results of measurements of the optical dispersion were communicated. Separation of normal and pathologicalG- andA-protein by column chromatography was possible. The dispersion constants and the parametersa ₀ andb ₀ according toMoffitt andYang of these preparations were measured. The relation of the results to conformation and specfity of pathological immunoglobulins are discussed.

     

Zur Bedeutung der pathologischen Proteinkomponenten im Liquor cerebrospinalis und im Serum von Patienten mit der subakuten Encephalitis nach Dawson-Pette-D?ring-van Bogaert

Zusammenfassung Die subakute Encephalitis vonDawson, Pette-Döring undvan Bogaert wird durch das Vorkommen von pathologischen Eiweißkomponenten im Bereich der 7-S- _SS-Globuline begleitet. Wo im Serum die Paraproteine immunoelektrophoretisch im kathodischen Gebiet dieser Globulinfraktion festzustellen sind, muß im Liquor cerebrospinalis auch die Aufmerksamkeit dem anodischen Teil der 7-S- _SS-Globuline gewidmet werden.

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Summary Subacute encephalitis described byDowson, Pette, Döring andvan Bogaert is associated with presence of pathological protein components in the region of 7 S _SS-globulins. In the blood serum of the patients it is possible to determine paraproteins in the cathodic segment of this globulin fraction. In the cerebrospinal fluid it is necessary to pay attention also to the anodic segment of 7 S _SS-globulins.

     

Isolierung von 19 S-Antikörpern durch Gelfiltration und Säulenelektrophorese

Zusammenfassung Es wird ein Verfahren zur Isolierung von -M-Globulin beschrieben, das in zwei Trennschritten zu einem weitgehend reinen Präparat führt. Nach der Fraktionierung von Human-Serum durch Gelfiltration an Sephadex G-200 wurde die makroglobulinhaltige erste Fraktion weiter durch Säulenelektrophorese aufgetrennt. Es gelang eine saubere Trennung von ₂-Makroglobulin und -Makroglobulin. In beiden Fraktionen fanden sich immunelektrophoretisch noch Spuren von ₂-Lipoprotein.Das Verfahren wurde zur Isolierung von Antikörpern gegen cytoplasmatische Antigene aus Humanleber verwendet. Die Antikörperaktivität der -M-Globuline wurde durch den Trennvorgang nicht beeinträchtigt.

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Summary A method for the preparation of -M-globulin is described, which gives a nearly pure substance in a two steps operation. After gel-filtration of human serum on Sephadex G-200, the first fraction containing the macroglobulins, was further separated by column electrophoresis. The ₂-macroglobulin was well sparated from the -macroglobulin. Only traces of ₂-lipoprotein were found in both fractions. The method was used for the isolation of antibodies against cytoplasmatic antigens from human liver. The separation procedure did not diminish the activity of the antibodies.

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Mit Unterstützung der Deutschen Forschungsgemeinschaft.     

Modulation of Ca2+-activated K+ channels by Mg2+ and ATP in frog oxyntic cells

Ca²⁺-activated K⁺ channels in the basolateral plasma membrane of bullfrog oxynticopeptic cells are intimately involved in the regulation of acid secretion. Patch-clamp techniques were applied to study the regulating mechanism of these channels. In the excised inside-out configuration, intracellular Mg²⁺ decreased channel activity in a dose-dependent manner. In the absence of Mg²⁺, administration of adenosine 5 triphosphate (ATP) to the cytoplasmic side also inhibited channel activity. On the other hand, in the presence of Mg²⁺, addition of ATP markedly increased channel activity. At a fixed concentration of free Mg²⁺ the Mg-ATP complex caused channel activation and shifted the dose response relationship between channel activity and the intracellular Ca²⁺ concentration to the left. A nonhydrolysable ATP analogue, adenosine 5-[,-imido]triphosphate (AMP-PNP) adenylyl [,-methylene]diphosphate (AMP-PCP), could not substitute for ATP in channel activation, but a hydrolysable ATP analogue, adenosine 5-O-(3-thiotriphosphate) (ATP[S]) could do so. Furthermore, application of alkaline phosphatase to the cytoplasmic side inhibited channel activity. These results demonstrate that Ca²⁺-activated K⁺ channels are regulated by Mg²⁺ and ATP, and suggest that a phosphorylation reaction may be involved in the regulation mechanism of these channels.     

Electrical properties of gap junction channels in guinea-pig ventricular cell pairs revealed by exposure to heptanol

Cell pairs were isolated from adult guinea pig ventricles to study the electrical properties of gap junction channels. The experiments involved a double voltage-clamp approach and whole-cell, tight-seal recording. Heptanol decreased the intracellular current, I _n, in a dose-dependent fashion. Before complete uncoupling, I _n showed fluctuations suggesting the operation of gated channels. In the presence of 3 mM heptanol, I _n showed quantal steps arising from spontaneous opening and closing of single channels. The IV-relationship of the channels was linear (range: ±95 mV). Analysis of current records revealed the following singlechannel conductances, _n: Mean value = 37 pS; median value = 33 pS. _n was insensitive to the non-junctional membrane potential (range: –90 to +10 mV). 3 mM ATP^4– in the pipette solution had no effects on _n, 6 mM ATP^4– produced a small decrease, and 6 mM ATP+0.1 mM cAMP^– an increase in _n. Channel transitions from closed to open state were variable (range of apparent time constants: 2.5–32 ms; mean: 11 ms).     

Receptors and G proteins as primary components of transmembrane signal transduction

Seven-transmembrane receptors signal through nucleotide-binding proteins (G proteins) into the cell. G proteins are membrane-associated proteins composed of three subunits termed , and , of which the G subunit classifies the heterotrimer. So far, 23 different mammalian G subunits are known, which are grouped in four subfamilies (G_s, G_i, G_q, G₁₂) on the basis of their amino acid similarity. They carry an endogenous GTPase activity allowing reversible functional coupling between ligand-bound receptors and effectors such as enzymes and ion channels. In addition, five G and seven G subunits have been identified which form tightly associated heterodimers. Upon activation by a ligand-bound receptor the G protein dissociates into G and G, which both transmit signal by interacting with effectors. On the G protein level, specificity and selectivity of the incoming signal is accomplished by G protein trimers composed of distinct subunits. On the other hand, many receptors have been shown to activate different G proteins, thereby regulating diverse signal transduction pathways.Abbreviations CT Cholera toxin - PT Pertussis toxin     

Die optische Rotationsdispersion isolierter Paraproteine

Zusammenfassung Die aus dem optischen Drehungsvermögen abgeleiteten Konstanten elektrophoretisch isolierterA-Paraproteine werden mitgeteilt. Die Dispersionskonstante _c weist keine Unterschiede zwischen den 3 ParaproteingruppenG,A undM auf. Der nach dem Verfahren vonMoffitt undYang ermittelte Parameterb ₀ wurde zu Schätzung des-Helixgehaltes benutzt. Er betrug in den 7 untersuchten Paraproteinen 0. Für den Parameter —a ₀ ergab sich ein Mittelwert von 276,0±35,1. FürG-Paraprotein wurde in früheren Untersuchungen ein solcher von 312,8±20,8, fürM-Paraprotein 217,9±26,7 gefunden. Der Mittelwertsvergleich zeigte Signifikanz der Konstantea ₀ für jede der 3 Paraproteingruppen.a ₀ beschreibt demnach gruppenspezifische Eigenschaften von Paraproteinen. Die für den Wert vona ₀ maßgeblichen strukturellen Voraussetzungen sind kaum bekannt. Sie werden am ehesten die die spezifischen Antigendeterminanten tragenden H-Ketten des Paraproteinmoleküls betreffen.

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Summary The constants of the optical rotatory dispersion of electrophoretically isolatedA-paraproteins are communicated. There is no difference between theG,A andM-paraprotein group with respect to the dispersion constant _c . The parameterb ₀ was measured according toMoffitt andYang. The-Helix-content calculated fromb ₀ of 7A-paraproteins was sero (0).The mean value of the parameter —a ₀ was 276±35,1. In earlier experiments it was found that —a ₀ forG-paraproteins is 312,8±20,8 and forM-paraproteins 217,9±26,7. The parametera ₀ of each group differs significantly from the others; in other words,a ₀ is group specific. The structural implications of these findings are discussed.

     

Differential induction of human monocyte transforming growth factorβ1 production and its regulation by interleukin 4

We have previously shown that trauma patients' monocytes which arein vivo activated by multiple injury-induced mediators have elevated transforming growth factor-beta (TGF) bioactivity. Interleukin-4 (IL-4), a Th₂ and B lymphocyte stimulatory factor, has been shown to inhibit monocyte production of a number of mediators both after lipopolysaccharide stimulation and after trauma-induced stimulation. However, IL-4 inhibitory effects appears to vary, depending on the mixture of inducing stimuli. Here we describe thein vitro IL-4 inhibition of human monocyte TGF bioactivity using several stimulation induction protocols: muramyl dipeptide stimulation alone, or after FcRI (CD64) cross-linking induction, interferon-gamma (IFN) priming, or trauma-generatedin vivo mediator induction. IL-4 suppressed both muramyl dipeptide-induced TGF bioactivity and TGF mRNA in a dose-dependent fashion and was most effective when IL-4 was administered at initiation of normal monocyte stimulation. Muramyl dipeptide (MDP)-induced increases in trauma patients' monocyte TGF bioactivity were also inhibited by high doses of IL-4 (25 ng/ml). FcRI cross-linking increased MDP-induced normal monocyte TGF bioactivity, but this increase could be consistently inhibited only by very high IL-4 concentrations (50 ng/ml). IL-4 did not consistently downregulate MDP-induced TGF bioactivity in IFN-primed monocytes. IL-4 can suppress monocyte TGF production, as well as other monocyte mediators, but its efficiency depends on the stimuli combination present in the microenvironment.     

Modulation of L-type Ca channel activity by P2-purinergic agonist in cardiac cells

The mechanism of enhancement of the L-type Ca current by a P₂-purinergic agonist adenosine-5-O-(3-thiotriphosphate) (ATPS) was studied by recording single channel activity from cell-attached patches on rat isolated ventricular cells using patch pipettes containing 110 mM Ba²⁺. The application of ATPS to the patch membrane through the pipette solution did not affect single channel activity. The addition of ATPS to the bath containing a depolarizing solution was ineffective due to the voltage dependence of the purinergic stimulation. Bath application of ATPS (100 M) to control 4-(2-hydroxyethyl)-1-piperazineethanesulphonic acid (HEPES) solution increased the amplitude of ensemble average currents both by decreasing the probability of a blank sweep occurring and by increasing the number of openings per non-blank sweep. The single channel conductance (17 pS) was not changed by ATPS. Both activation and inactivation curves were shifted towards hyperpolarized potentials by about 10 mV under P₂-purinergic stimulation. Since ATPS increased channel activity when applied via the bath, it must be supposed that a diffusible messenger is involved.     

Fc receptor-mediated signal transduction

Receptors for the Fc domain of IgG (FcRs) on leukocytes mediate a pleiotropic response following cross-linking by immune complexes. Signaling events following cross-linking of B and T cell antigen receptors, FcRs, and FcRs share common elements. In each, signaling is initiated by receptor cross-linking by antigen or immune complexes and results in the activation ofsrc family kinases and ZAP-70-related tyrosine kinases, which associate with members of the receptor complex. Subsequent events include phosphorylation on tyrosine of multiple cellular substrates including phospholipase C1 and PI3-kinase. The [Ca²⁺]_i flux is an event secondary to phospholipase C1 activation. Protein tyrosine kinase inhibitors block both early events such as [Ca²⁺]_i flux and the later effects of cytokine release and cellular proliferation.     

Chloride channels in cultured human skeletal muscle are regulated by G proteins

The regulation of Cl^– channels in human myoballs by G proteins was studied using whole-cell and inside-out patch recordings. After perfusion of the cell with 0.1 mM GTP[S], the specific Cl^– conductance, G _Cl, at standard resting potential (–85 mV) was increased from 5.9 S/cm² to 103 S/cm², and the kinetics upon stepping the potential to positive values was changed from an activating current with very slow inactivation to a fast inactivating current with no potential-dependent activation. These effects were not affected by the simultaneous blockade of several signal cascades involving G proteins. Addition of the protein kinase blockers PKI (25 M), H8 (10M), or of the phospholipase-A₂-blocking agent quinacrine (10 M), had not much influence on these GTP[S] effects. Buffering of the intracellular Ca²⁺ concentration (0.1 M) or addition of the Ca²⁺/calmodulin antagonist trifluoperazine (50 M) was also without effect. Pre-incubation of the cells with pertussis toxin or with cholera toxin did not change G _Cl. In excised inside-out patches voltage-clamped at –85 mV, application of GTP[S] influenced the intermediate Cl^– channel, the Cl^– channel type having the highest density in these cells, by increasing the number of transitions in a half-conductance state. The probability of the channel being in one of the two conducting states rose from 0.015 to 0.67, and the kinetics of the single-channel currents was changed so that, on average, it was similar to the whole-cell current kinetics seen after application of GTP[S]. It is concluded that a G protein is directly interacting with these channels.     

Increase in TCRγδ T lymphocytes in synovia from rheumatoid arthritis patients with active synovitis

To determine the relative presence of TCR+ and TCR+ T cells in synovial tissue from patients with various types of inflammatory synovitis and in tissues from patients with a number of chronic T cell-mediated conditions, we stained frozen tissue sections with monoclonal antibodies in indirect immunofluorescence assays. In tissues obtained from patients with chronic T cell-mediated granulomatous conditions (Wegener's granulomatosis, lymphomatoid granulomatosis, granuloma annulare, Langerhan's cells granulomatosis, pigmented villonodular synovitis, Takayasu's arteritis, and talc granulomatosis), the T cells present were predominantly TCR+, without an increased presence of TCR+ cells. In contrast, 6 of 14 (43%) synovia from patients with rheumatoid arthritis (RA) showed increased TCR+ T cells (3–10 cells/hpf). The RA synovia with increased TCR+ cells present had an increased tissue inflammation score compared to RA synovia with few TCR+ cells [18.6±5.8 versus 11.6±4.2 (mean±SE),P<0.05]. In contrast, synovia from patients with osteoarthritis, systemic lupus erythematosus, and trauma did not show an increased presence of TCR+ T cells. Thus, in cellular inflammatory infiltrates the presence of increased TCR cells is not a component of noninfectious granulomatous inflammation but is found in approximately 40% of RA synovia with high levels of inflammation.     

Charge movement and calcium currents in skeletal muscle fibers are enhanced by GTPγS

G-proteins play several regulatory roles in the cell. They can modulate ionic channels directly or in association with second messengers. In skeletal muscle, G-proteins modulate the activity of calcium channels either by acting directly on the channel and/or through a cAMP-dependent phosphorylating mechanism¹⁹. The activation of G-proteins by GTPS can also induce force generation in skinned fibers⁷. In this paper we studied the effect of GTP-S on charge movement and calcium currents (I_Ca) in rat and frog skeletal muscle, using the Vaseline gap technique. We observed an increase in both charge movement and I_Ca after the intracellular addition of 10–100 M GTPS. GDPS did not have any effect. Addition of protein kinase A catalytic subunit increased the I_Ca, probably through a phosphorylation process, but did not modify the charge movement. This suggests that protein kinase A and GTPS are acting on different sites of the channel. It can be speculated that G-proteins may have a regulatory role in the excitationcontraction coupling mechanism by a direct effect on charge movement.     

The role ofγδ T cells in the normal and disordered immune system

Summary A small population of T cells does not express the conventional T cell receptor characterized by the and polypeptide chains (TCR) but instead, two polypeptides termed and (TCR). This alternative receptor is able to recognize antigen. It appears early in T cell ontogeny, but its role in the thymus prior to the availability of TCR remains unclear. In selected sites such as skin or gut TCR predominates in mice which might suggest a role of T cells in the first line of defense against infection, T cells secrete lymphokines and display cytotoxic activity. However, their activation requirements may differ from what is known for T cells since MHC-nonrestricted and also CD4 and CD8 negative T cells have been described. Preferential activation by mycobacterial antigens possibly indicates a special repertoire of the T cells. In various diseases slightly increased numbers of T cells were found, but these preliminary studies have not yet provided evidence for a major pathogenetic role of T cells.List of abbreviations C constant region (immunoglobulin or TCR gene segment) - CD4 cluster of differentiation 4 (mainly on helper cells) - CD8 cluster of differentiation 8 (mainly on cytotoxic cells) - D diversity region (immunoglobulin or TCR gene segment) - DNA desoxyribonucleic acid - IL2 interleukin 2 - J joining region (immunoglobulin or TCR gene segment) - kD kiloDalton - MHC major histocompatibility complex - NK natural killer (cells) - RA rheumatoid arthritis - TCR T cell receptor - V variable region (immunoglobulin or TCR gene segment)     

Intracellular ATP and GTP are both required to preserve modulation of N-type calcium channel current by norepinephrine

Norepinephrine (NE) inhibits voltage-dependent calcium channels of sympathetic neurons. We investigated the role of intracellular nucleotides in this inhibition for clues to receptor-channel coupling mechanisms. Both ATP and GTP are required to preserve NE responsiveness during whole-cell dialysis. The response to NE was gradually lost in bullfrog sympathetic neurons dialyzed with GTP as the only nucleotide, ATP only, or no nucleotides. Replacing ATP with ATP[-S] resulted in spontaneous modulation of calcium channel current, possibly because of production of GTP[-S]. The nonhydrolyzable ATP analog p[NH]ppA could substitute for ATP to preserve NE responsiveness. The protein phosphatase inhibitors okadaic acid and calyculin-A did not affect NE inhibition of calcium channel current, or recovery from that inhibition. These results suggest protein phosphorylation is not involved in the inhibition of calcium channel current, but binding of ATP to some intracellular site is required for the coupling of adrenergic receptors to calcium channels.     

Untersuchungen über die spezifische und quantitative Erfassung des Liquor-γ-Globulins mit der Zinksulfatfällung

Zusammenfassung Die Frage der quantitativen und elektiven Erfassung des Liquor--Globulins mit der vonRoboz u. Mitarb. beschriebenen Zinksulfatfällung wurde an Modellversuchen mit reinem -Globulin und Albumin und an der elektrophoretischen Auftrennung des mit Zinksulfat aus Liquor präzipitierten Proteins untersucht. Aus reinen -Globulinlösungen wurden in Abhängigkeit zu der in Ansatz gebrachten -Globulinmenge nur 18–46% gefällt. Das Elektrophoresediagramm der mit Zinksulfat gefällten Liquorproteine zeigte, daß neben einer Anreicherung des -Globulins eine Fällung sämtlicher Liquorproteine zustande kam. Die elektrophoretische Auftrennung der im Überstand der Fällung verbliebenen Eiweißkörper ließ neben den übrigen Fraktionen noch eine deutliche -Globulinbande erkennen. Eine elektive und quantitative Fällung des Liquor--Globulins mit der Zinksulfatmethode konnte demnach nicht nachgewiesen werden.Herrn Dozent Dr.H. Bauer danke ich für die Anregung und Unterstützung bei Durchführung dieser Untersuchungen.     

Riluzole specifically blocks inactivated Na channels in myelinated nerve fibre

The effects of 0.15–250 M riluzole, a novel psychotropic agent with anticonvulsant properties, were studied on voltage-clamped nodes of Ranvier of isolated nerve fibres of the frog. When added to the external solution, the drug rapidly and reversibly inhibited both K and Na currents with an apparent dissociation constant of 0.09 mM. The riluzole-induced decrease of these currents was not use-dependent. At concentrations up to 100M, the drug had no noticeable effect on the time course of Na current inactivation nor on the shape and the position along voltage axis of the Na conductance/voltage relationship. On the other hand, it induced substantial shifts towards negative voltages of the steady-state Na inactivation/voltage curve. From these results, according to the modulated-receptor model, an apparent dissociation constant of 0.29 M could be calculated for riluzole-induced blockage of inactivated Na channels. The recovery from Na current inactivation was also affected by the drug. It is concluded that riluzole is a highly specific blocker of inactivated Na channels, which is more than 300 times more effective on these channels than on K or resting Na channels.     

Antibody response inPlasmodium vinckei malaria after treatment with chloroquine and adjuvant interferon-γ

The antibody response of mice infected withPlasmodium vinckei after treatment with chloroquine either alone or in combination with interferon- (IFN-) was determined. Sequential serum samples were drawn from BALB/c mice receiving either 240 g chloroquine on the day of infection or 120 g chloroquine plus 10⁴ units IFN- daily for 11 days beginning on day 3 prior to infection. Mice treated with additional IFN- showed an early induction of IgG2a response and a reduction in IgG1 antibodies as detected by the immunofluorescence technique at between 10 and 16 days after infection as compared with mice treated with chloroquine alone. Thus, IFN- may partly exert its antimalarial activity via the induction of IgG2a antibody formation. At 4–6 weeks after infection, when mice from both groups resisted homologous re-infection, the predominant antibody isotypes found in both groups were IgG1 and IgG2a. Serum samples obtained from mice in both treatment groups at 6 weeks after infection were used for serum transfer experiments. When parasitised erythrocytes were preincubated with such immune serum, a retardation of the course of parasitaemia by 2 days was observed.